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"We all use math every day. To predict weather, to tell time, to handle money. Math is more than formulas and equations: it's logic, it's rationality, it's using your mind to solve the biggest mysteries we know."

A Police Procedural revolving around an Odd Couple of crime-solving brothers. Don Eppes (Rob Morrow) heads a team of FBI investigators called on to solve the exceptionally sensitive and baffling crimes that happen in Los Angeles about once a week. To solve these highly complex crimes, he invariably turns to his brother, Charlie (David Krumholtz), a college professor and mathematical prodigy, who applies pure mathematics to the task of solving crimes.

Ultimately, math conquers all... though on the way, Charlie usually faces a crisis of faith stemming from the fact that, while he's a mathematical genius, he is emotionally immature, with only a very slight understanding of human motivation. Balance is restored via the assistance of his father Alan (Judd Hirsch, a veteran of three other TV series produced by Paramount) and physicist colleague Larry (Peter MacNicol). Larry generally advises him to steer clear of messy human-interaction problems, while Alan nudges him toward a better understanding of human nature.

The show finished its sixth and final season in 2010.

The show's storylines were supposedly inspired by actual cases.


7his series provides examples of:

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    A-C 
  • 555: The fifth season finale uses the IP address 275.3.6.28.
  • Absent-Minded Professor: Both Charlie and Dr Larry Fleinhardt are prone to this. Charlie gets better as the series progresses, but Larry is prone to being so deep in contemplation of either physics, math, or philosophy that he forgets what's going on around him.
    Larry: Let me ask one thing. When we met just now, was I coming out or going in to the library?
    Charlie: Coming out.
    Larry: [sighs] My memory is a memory. All right. [starts back inside]
    Charlie: [yells] Larry, you were coming out!
  • Accidental Murder:
    • In the episode "Noisy Edge", which involves a crashed ultralight aircraft, it turns out that the pilot's son made some adjustments to the rudder that the pilot didn't know about, and when he went out on a flight without telling anyone, the adjustments caused him to overcorrect on his flight, causing him to crash.
    • The opening scene of "Rampage", involving a man busting into the FBI office and shooting everything up, ends with a fusillade of bullets, and one man dead: a suspected pedophile the team was interrogating at that moment. It turns out that Colby's bullet was responsible, on account of the bullet going straight through the attacker's shoulder, through the office window, and into the pedophile's head.
    • "Dreamland" involves a company trying to develop a less-lethal directed energy weapon, but the project proves to be more unworkable than anticipated. Eventually overconfidence and pressure from losing funding and being shut down caused the team to take too many risks and even use themselves as test subjects, which turns ugly when the weapon proves too lethal.
  • Action Girl: Terry Lake, Megan Reeves, Liz Warner, and Nikki Betancourt.
  • A Fistful of Rehashes: One killer started doing this to try and eliminate gangs after his young son was murdered by gangsters; he would kill a member of one gang and make it look like the rival gang did it, so the victim's gang would retaliate against said rival, who retaliates back, and so on, often with 5 or 6 shootings at least stemming from that one murder. By the time the crew catches up with him, his actions have resulted in the deaths of about 150 people and he very clearly has gone insane from the guilt and grief and winds up killing himself with his handgun.
  • Affectionate Nickname:
    • Don refers to Charlie as "Buddy" or "Chuck" from time to time. As shown in The Tag for "Backscatter", Charlie has issues with the latter nickname on occasion.
    • Colby's nickname for Charlie is "Whiz Kid".
    • Don is referred to "Donnie" from time to time, mainly by Alan.
  • Agents Dating: Don and Liz, before the relationship ended in season 4.
    • Prior to the star of the series, Don dated Terri Lake in the academy and was engaged to Kim Hall.
  • A.I. Is a Crapshoot: Briefly holds Amita hostage and turned out to be fake.
  • Air-Vent Passageway: Not "escaping" anything, but the "steam tunnel spelunkers" aspects shows up when it is revealed that Larry has been living in the tunnels on campus for awhile.
  • The Alleged Expert: Zigzagged in "Identity Crisis". The fingerprint technicians convicted a man due to thinking that an upside down index fingerprint was a thumbprint. While there are some commonalities that make the mistake understandable, the main technician is kind of a Smug Snake and is reluctant to admit how much room for error there is in her work.
  • All for Nothing:
    • Season 3 episode "Democracy" involves one of Charlie's mathematician friends being killed, along with several of her associates, on account of the research they were doing, which could possibly be used to rig voting machines and elections. The prime suspect escapes prosecution due to one of his subordinates taking the fall, but Charlie takes his friend's research and publishes it in the paper, allowing the state legislature to know exactly what to look for in the machine's software and stymie any attempts to rig the elections.
    • Season 5 episode "Sneakerhead" involves the theft of $250,000-value sneakers. The victim ends up basically stealing them back, but when he goes to look for them in the end, it turned out that his son found them, thought they were a birthday present for him, and wore them out in the rain.
    • Season 5's "Cover Me" involves Charlie coming up with a convoluted plan to disrupt the supply of a new drug, known as Hawaiian Ice, with the intention of preventing it from being able to become mainstream. While it actually works with regards to that particular drug, Charlie subsequently learns that rather than leading to an overall reduction in drug crime, the lack of this one drug just led to an increase in the trafficking of other drugs to make up for the void in the market. Don tries to convince him that he still made an impact, even if it wasn't exactly what he was hoping for, but Charlie is skeptical.
  • All Guys Want Cheerleaders: In the episodes "Dark Matter" and "The Running Man", Megan asks Colby what he was into during high school and college, and both times his answer is "Cheerleaders".
  • Alliterative Name: Susan Stone in "Jack of All Trades".
    • Margaret Mann, before she married Alan Eppes.
    • Becky Burdick in "Prime Suspect".
    • Bill Bryce in "High Exposure".
    • Clayton Caswell in "Frenemies".
    • Steve Savard in "Disturbed".
    • Darren Drew in "Dreamland".
  • Alliterative Title: Double Down, Hollywood Homicide, Pay to Play, Friendly Fire and Arm in Arms.
  • All Your Base Are Belong to Us:
    • Season 2 episode "Rampage" starts with a man charging into the FBI office and shooting bullets around, almost catching Charlie in the crossfire.
    • In "Chinese Box", a former contractor holds David hostage inside an elevator in the FBI building.
  • Altar the Speed: In the middle of Charlie and Amita's wedding preparations, an invitation for a visiting professorship in Cambridge comes up for the two of them. Not wanting to rework or postpone their plans or burden their friends with travel issues, they decide to get married the very next day.
  • Alternate Reality Game: Chain Factor, an addictive little Flash game which went rather deeper, including clues scattered throughout one episode, online sites, and the Los Angeles subways to unlock various power-ups.
  • Always Gets His Man: Don Eppes.
  • Amazingly Embarrassing Parents: Alan Eppes can be this at times.
    • When Amita's parents come to California to meet Charlie, they invite a family friend — a young man about Amita's age — to join them for dessert while out to dinner with Charlie. Amita initially completely misses what's going on because she knows her friend is gay and therefore just doesn't connect him with the idea of a relationship, even a theoretical one; when Charlie pointedly asks her if her parents know the friend is gay, she realizes what they were trying to do and is mortified.
  • Ambiguously Jewish: The Eppes family were this for the first couple of seasons; the third-season episode "Provenance" established them as non-observant Jews, although in the fifth season, Don starts going to a synagogue and exploring the faith more.
  • Amicable Exes: Don and Liz. Things are awkward for them for a couple episodes after they break up in season four, and then everything's fine. Liz even offers advice to Robin when she's having a fight with Don.
  • Amoral Afrikaner: Subverted in one episode. A bank is robbed and a number of safety deposit boxes are emptied. The boxes belong to a number of shady individuals, including a South African mercenary, and are suspected to have contained very incriminated evidence. In the end, the FBI determines that the whole thing was a Kansas City Shufflethe Afrikaner mercenary was behind it, but he was doing it to ruin the corrupt bank owner who was responsible for the death of the mercenary's brother. The merc turns the evidence over to the FBI and gives the stolen money to charities supported by the burned down runaway house that his firefighter brother died trying to save.
  • Analogy Backfire: The Director of the Los Angeles Homeland Security Office refuses to shut down his series of anti-terror drills that seem to be the target of a saboteur, even after one attack puts six people in the hospital. When Don and Megan attempt to talk it out with his assistant, this exchange occurs.
    Director's assistant: Stop the drills now, it's like turning the Titanic.
    Megan: The Titanic hit an iceberg!
  • And I'm the Queen of Sheba: One episode has Megan quipping: "If this is a Muslim terrorist, I'm a Japanese schoolgirl!"
  • And Starring: Peter MacNicol. In previous seasons, it was Diane Farr that was credited this way.
  • Animal Wrongs Group: "Animal Rites" has one of these, who accidentally killed a professor (when his partner learned of it later, he was appalled). It turns out that he is schizophrenic and believes animals have greater "spirits" than humans; he acted independently from the main animal rights group.
  • Annoying Younger Sibling: Charlie is stated to have been this to Don when they were kids, largely because Charlie, as a Child Prodigy, took up a lot of attention from their parents and occasionally made Don feel stupid by comparison.
  • Answer Cut: One episode has Nikki ask a question of an awards director, cuts out (in a broadcast, this is where there would be a commercial), and then cuts back in for Nikki's reaction to the director's answer, literally cutting out only the extremely brief moment where the director actually answers the question.
  • Anti-Hero: Ian Edgerton.
  • Are You Pondering What I'm Pondering?: Charlie and Colby have one of these in "Brutus" while trying to determine the identity of the mastermind behind a series of assassinations.
    Colby: Feels to me like we're missing something so obvious we must've forgotten about it. You know, can't see the forest for the -
    Charlie: - Tress ("Eureka!" Moment ensues) Are you thinking what I'm thinking?
    Colby: No.
    • Rather adorably, in the next scene, Charlie still allows Colby to share credit for the breakthrough.
  • Arranged Marriage: The pilot reveals Amita's parents tried to set her up in one of these. Her "fiance" is back in India, while Amita moved to the US when she was little. When asked if she plans to marry him, she replies that she won't, as he doesn't like the guy at all. In a later season, Amita and Charlie start dating. However, Amita admits to Charlie that the fact that he's not Indian will be a problem for her parents. At a dinner with her parents, an old friend of Amita's shows up at the invitation from her parents in an obvious attempt to set them up. Only one problem-the guy is gay. Also, they reveal that, after meeting Charlie face-to-face, they have warmed up to him.
  • As Himself: Penn Jillette of Penn & Teller guests stars in the season five episode "Magic Show'.
    • Buzz Aldrin appears in the third season episode "Killer Chat".
    • Three 6 Mafia appear as themselves in the season four episode "Pay to Play".
  • Asshole Victim: Frequently. Occasionally paired with Sympathetic Murderer, but in other cases, the victim is just as bad as the killer.
    • One example is in "Killer Chat", involving a Knight Templar Serial Killer going after pedophiles. The climax has the team catch the killer with another pedophile held hostage, and when the victim thanks David after the standoff, David snaps at the pedophile to shut up.
    • "Rampage" starts with the team working on a pedophile case with the suspect in interrogation. Said pedophile becomes a victim of collateral damage and the only fatality when someone else bursts into the office and starts shooting up the place.
    • In "Dark Matter", it's revealed that four of the victims in a school shooting were targeted by one of the shooters because they were all involved in setting her up to be raped. Ironically, the actual rapist wasn't among those shot (presumably the shooter couldn't find him), though he ends up getting arrested as it turns out one of the accomplices who died in the shooting had kept evidence of the rape on his phone.
    • The series finale is just a pileup of these. Don loses his gun during an arrest, and it becomes a symbol for people who feel the police aren't protecting them. The three people actually killed are two drug dealers and a chronic drunk driver; there are also near-misses on a man who's been abusing his ex-girlfriend and a bully who's been terrorizing his neighbors.
  • Author Filibuster: In "Money for Nothing", the plot stops dead in its tracks for five minutes so Charlie and a guest star can lecture Colby on the wonders of microcredit.
  • Aw, Look! They Really Do Love Each Other: It's implied more than once that the entire series is this for Don and Charlie:
    Alan: I was afraid before [their first case] that you had grown so far apart that I was the only thing you had in common. I figured after I died, you might spend years without seeing each other, but to tell you the truth, I'm not worried about that anymore.
    • "Breaking Point" also plays out the trope quite clearly. Don spends the entire first half of the episode furious with Charlie for doing a TV interview about a case (which is against FBI rules). However, when Charlie becomes a target, Don completely forgets that he was mad and is only upset that Charlie didn't feel like he could tell Don what was going on.
    • David and Colby also have several of these moments throughout the series. Especially notable when it happens early Season 4 (when their relationship is strained), but even apart from that, the occasional disagreements between them and the fact they often edge in Vitriolic Best Buds territory makes it a case of this in the moments when they really do show how much they care.
  • Awesomeness by Analysis:
    • Subverted. The super-brain Charlie Eppes tries, among other things, golf and sniping, and learns that knowing the math simply isn't enough. It requires some kind of instinct or gut feeling to get it right.
    • The episode "Arm in Arms" has one of Charlie's engineering colleagues identify an explosive design flaw in a new model of assault rifle, from just one look at the plans. He's right.
  • Back for the Dead: Simon Kraft died in the Season 5 episode "Trouble in Chinatown" after being run over by a car.
  • Back-to-Back Badasses: Don Eppes and Billy Cooper in "Man Hunt".
  • Backwards-Firing Gun: An inadvertant version occurs in the Season 6 episode "Arm in Arms" due to a design flaw in an automatic weapon: in an attempt to keep the weapon's weight down so it would be easier to carry, the designer made the barrel wall too thin to withstand the heat and pressure buildup that comes from continuous firing, causing the barrel to explode if the gun is in operation for too long. The owner of one of said guns learns this the hard way when his gun literally blows up in his face; he is killed by a piece of shrapnel being driven into his neck by the force of the explosion.
  • Badass Bookworm: As of Season 5, Charlie can SO kick ass. One FBI training course and BAM!, he has a gun. Subverted in a later episode where it's shown that yes, he can target shoot, but that doesn't automatically make him good in a real fight. (Target shooting was also his only success in that course: before his jaw-dropping performance on the range, he failed miserably at vehicle pursuit, hand-to-hand, and dynamic entry.)
    Sinclair: It's a lot different when they're shooting back, okay?
  • Badass in Distress:
    • Colby in the Season Four premiere when he is being tortured by Lancer.
    • Don is briefly this in "Graphic" when he is headbutted and briefly held hostage by a suspect and it takes David's intervention to keep him from being shot.
  • Badges and Dog Tags: Colby Granger was an Army CID investigator before joining the FBI. It was during this time he was pinned after an explosion, from which Dwayne Carter saved his life. His first appearance as the FBI New Meat highlights the clash in this mentality, as he tries to wave his gun around in a gang lair and David has to defuse the situation.
  • Bait-and-Switch:
    • "Harvest" starts with a young Indian girl named Santi being discovered hiding in a blood-covered hotel basement, where an underground kidney removal had gone wrong. Santi asks the FBI to find her sister, and they discover a dead South-Asian Jane Doe in a hospital morgue whose blood matches the blood in the hotel basement. When Megan and Amita break the news to Santi using a picture of the body as evidence, she starts crying and muttering "no". That's when Santi reveals that no, this isn't her sister, this is one of her friends, revealing that there were two more girls besides Santi and her sister who were selling their kidneys on the black market at that hotel.
    • In the middle of "Backscatter", a bank manager is accosted by some goons and stuffed into the back of a truck. He starts pleading that he hasn't told the FBI anything... only to look up to see the FBI agents he'd met earlier, who had accosted him to get him out of sight of the Russian mob, who they figured out are blackmailing him.
    • The first half of "Jack of All Trades" has Agent McGowan, who is investigating Charlie and Don during the former's appeal to regain his security clearance, recommending to the decision board that Charlie be rejected and disciplinary action brought up against Don for his more maverick tactics. When the decision is finally made, it turns out that the board disagreed with McGowan and reinstated Charlie's clearance.
  • Bait-and-Switch Tyrant: Mildred Finch in Season 3, as the new division chair of Charlie's department. She initially starts off getting on Charlie, Larry and Amita's cases for a number of issues, but provides insightful expertise in several FBI cases and soon warms up to the group (even dating Alan for a spell).
  • Bald of Authority: David Sinclair. Although not technically a leader, he is Don's second-in-command.
    • Don gives him the lead on a few projects, and he also becomes the head of the unit when Don is injured in "The Fifth Man".
  • Balkan Bastard: Slobodan Rodovic (Michael Khmurov), a Serbian war criminal, who not only stabs Don, nearly killing him, he is also wanted for ethnic cleansing in the Balkans during the war and the armed robbers were targeting him in revenge for wiping out their village in Croatia.
  • Baseball Episode: In the episode "Hardball", the team deals with the murder of a minor league player, which brings up old memories for Don, as he himself was a minor league player before he joined the FBI.
  • Batman Gambit: Charlie proved to be pretty good at this in episodes such as "Prime Suspect" and "Primacy". His strategies for trapping criminals include working out their plan so he could predict their course of action, and setting everything up so that to the criminal it seems everything is going according to plan, up until the point the trap is sprung.
    • One example can be found in "Backscatter". With the bank manager being held hostage by a Russian mob hacker who's plundering his systems, he's able to get a look at the hacker's phone and send the number to the FBI. Charlie then calls the hacker to threaten him, leading the hacker to call his boss to ask what he should do next, thereby leading the FBI right to the boss, while said boss, believing that his blackmail of Don has kept Charlie out of the FBI loop and Charlie is acting on is own, remains none the wiser.
  • Bavarian Fire Drill: The fifth season's "Jack of All Trades" features a criminal who is basically a master of this. He can fake his way into any job simply by turning up the charm. When he's finally captured for the first time, he escapes from jail by pretending to be an attorney.
  • Be as Unhelpful as Possible: Averted in the episode "Tabu", when a rich father finds his Paris Hilton Captain Ersatz daughter has decided to go all Patty Hearst. He rushes into the station, takes on look at the TV paused on a shot of his daughter, and says he'll do anything he can to help the police. When the FBI Agent remarks that he's being remarkably helpful, he says that the sooner they get his daughter home safe, the sooner he can prepare a defense.
  • Be Careful What You Wish For: Alan's side plot in "Sneakerhead" has him taking on Charlie and Larry's lab as a class to get his lab credits at CalSci. Little did he know that the class in this case requires manual labor.
  • Beeping Computers: Most user interfaces seem to make an unusual amount of beeping, whining, and chirps as the user scrolls and clicks.
  • Believing Their Own Lies: The Art of Reckoning had a mob killer who wanted to make a confession, but while he passed the polygraph and even an MRI scan, the confession didn't match the facts. It turned out he'd been so horrified by the crime (which he hadn't even been able to commit) that he unwittingly created a false memory of things playing out better (many of the details he thought he remembered were actually drawn from an unrelated crime he had also been involved in) and genuinely believed that the story he was telling was an accurate recollection of the event. It's only when Charlie and Larry pick up on a detail that doesn't make sense and directly challenge him on it that he finally breaks through the mental barrier and remembers what really happened
  • Berserk Button: Threatening or hurting Charlie is a surefire way to piss off Don.
  • Beware the Nice Ones: The 1st-season episode "Uncertainty Principle" has the FBI going after a robbery team called "the Charm School Boys" on account of how polite they are during their heists. The FBI manage to intercept them as they are leaving another bank... only for their backup to show up loaded for war.
  • Beta Couple: Larry and Megan.
  • Big Brother Instinct:
    • Don towards Charlie. Amusingly, big brother Don also works for "Big Brother". But then in this case, Big Brother is also your friend.
      • As a frequent consultant for the NSA (National Security Agency), Charlie works for "Big Brother" as well.
      • Don also acts like a big brother to the entire team. And the other members of the team often treat Charlie like a little brother.
    • In "Robin Hood", the perp's brother was indirectly killed by an arson plot masterminded by a corrupt bank president who ran a bank with seedy customers. The perp proceeded to avenge his brother by robbing the bank to expose the president's misdeeds.
  • Big Disaster Plot: Thirty-Six Hours, which has the team dealing with the aftermath a massive train accident. The main plot involves the agents and Charlie attempting to rescue trapped passengers, while a secondary thread follows the investigation into the cause of the crash.
    • Train crashes were also the subject of an earlier episode, Sabotage, though none of those incidents were of the same scale. The one that the FBI ultimately foiled, however, quite possibly would have been a massive disaster if the saboteur had been able to carry out his plan.
  • Billy Needs an Organ: The episode "Harvest" involves a group of Indian girls brought to the U.S. to sell their kidneys to a black-market organ ring. Two girls and one recipient end up dead, and a third girl just barely dodges being killed as well.
  • Bland-Name Product: CalSci to Caltech. Though the latter is actually an inspiration.
  • Bollywood Nerd: Amita, who is of Indian descent and a computer genius.
  • Bond One-Liner: Colby gives one in "Harvest". During the investigation of an organ trafficking crime, he and David pursue a suspect who is an ambulance driver, only for him to crash and kill himself in the chase.
    David: Paramedics are on their way.
    Colby: Yeah? Well, maybe they can check and see if he's a donor.
  • Bottle Episode: There are a few episodes of or bordering on this type in Season 4, largely owing to the fact that Tony Scott blew a large portion of the entire season's budget just on the season premiere.
    • The most notable example is "Chinese Box". As the episode takes place inside FBI headquarters, most of the sets were pre-existing, and the few that weren't were very simple (a sparsely-furnished apartment, a storage unit). It did feature a few guest stars (Chris Bruno, Enrico Colantoni), but no huge names.
    • "End Game" was also shot largely on existing and/or simple sets and had very little in the way of special effects.
  • The Boxing Episode: In the episode "Contenders". One of David's old friends is involved in the death of an MMA fighter (the boxing of the present).
  • Brains and Brawn: The two Eppes brothers, with Charlie being the brains and Don being the brawn.
  • Brief Accent Imitation: In "Bettor or Worse", David pretends to be a package delivery man with a Caribbean accent to get a suspect's father to open the door to his house. This way, the FBI can get him outside so they don't accidentally hurt him while they raid his house to search for the suspect.
  • Buffy Speak: Sometimes used when describing Charlie's equations.
    Megan: Well, there's always Charlie's inequality... bounding... thing.
    Colby: There is always Charlie's "inequality bounding thing".
  • Bunny-Ears Lawyer: Larry is a highly eccentric scientist who, among other quirks, has no permanent residence from mid-Season 2 onwards, only eats white food, and once gave up all his possessions and spent several several months in a monastery. However, since the latter came about after he got to go into space, he's clearly qualified enough to act however he wants.
  • The Bus Came Back:
    • Larry comes back in The Art of Reckoning after being in space as Peter MacNicol returned from his 24 and fully returns to full cast in the season four premiere.
    • Megan comes back in the season three finale after Diane Farr returns from maternity leave.
  • Bus Full of Innocents: "Jacked" centers around a group of con men taking over a tour bus and taking the passengers hostage for ransom, threatening to execute them if the ransom isn't paid by a specified time, including shooting one hostage to prove they're serious. Eventually the FBI realizes the whole thing is all based in illusion - the "hostage" was actually a secret co-conspirator and his supposed shooting was staged - and they're able to free the hostages unharmed.
  • By-the-Book Cop: When Don is talking to his therapist, Bradford, he mentions (in a complimentary way) that he sees David Sinclair as this. David's actions throughout the series generally support this assertion.
    Don: The thing I admire about him is, the rules don't really bother him. I mean, he's the kind of guy that just somehow - he gets it done.
  • Call-Back: Several.
    • "End Game" and "Arrow of Time" get special mentions for this. Both episodes were call-backs to earlier episodes, but unlike the standard two-parter, it wasn't consecutive. "End Game" is a half a season after the setup episode "Thirteen", and "Arrow of Time" is a full two seasons after "Spree/Two Daughters".
    • Season 5 pilot episode "High Exposure" has a call-back to the season 1 episode "Noisy Edge", where the same algorithm is used to track flight paths to find missing aircraft.
    • Fifth-season episode "Disturbed" uses an equation to track down a serial killer, the very same one used in the first episode "Pilot". David even remembers it and is the one to explain the math.
    • At the end of "Growin' Up", Nikki and Colby remind David about one more piece of paperwork that needs catching up: his physical training. They bring out one of the counterfeit Primer sneakers from the "Sneakerhead" episode the season before.
  • Calling the Old Man Out:
    • Megan does this at one point to a millionaire who acts incredibly cold and distant towards his own daughter, though it is more of a Freudian Excuse due to problems with her own father.
    • Don's not above doing this to powerful people if he thinks they deserve it.
  • Can't Believe I Said That: In one episode, Colby notes that with a new piece of evidence, a lot of things in their case are starting to fall into place. How does he express this?
    Colby: A equals B equals C equals D; it's like one of Charlie's equations. (Beat) I can't believe I just said that.
  • Can't Kill You, Still Need You: Referenced in one episode when an escaped prisoner kidnaps the family of the man he blames for his downfall; the team initially assumes his intention is to lure the man to him so he can kill him, but Charlie later determines that he's actually trying to capture him alive (because he believes the man has valuable information he wants). This ultimately plays a critical role in their handling of the situation.
  • Can't Stay Normal: After Charlie's security clearance is revoked at the end of season 4, he has a chance to return to his normal life of academia. But he keeps getting pulled into cases, and even begins seeking out crime to solve by consulting for the LAPD, and eventually admits that he's bitten by the crime-solving bug.
  • The Casino: The episode "Double Down" revolves around card counting in a casino. Larry is revealed to be a former card counter, and he, Charlie, and Amita gamble at a casino to experience the mindset for themselves.
  • Catchphrase: "Everything is numbers." Or, perhaps, "everything is numb3rs."
  • The Cameo: The season 2 episode "Dark Matter" features well-known Broadway actress Marin Mazzie as the mother of a suspect. She appears in one scene and has only two lines.
  • Celebrity Is Overrated: Skyler White in "Obsession", as she is clearly unhappy with Paparazzi trying to get pictures of her in her own home, as well as mentioning her husband possibly having an affair with his co-star. She mentions that she's treated like a normal person in her hometown, as she is thinking of moving back there.
  • Celebrity Paradox: At the end of Season 3 Episode 7, Alan tries to cheer up Don, who has just revealed to his dad and brother that his girlfriend had dumped him a week prior, by finding something fun to watch on TV. What we hear from the TV is the theme from the 70's sitcom Taxi. Alan is played by Judd Hirsch, who was the main character on Taxi.
    • It's established multiple times that the Star Trek series exists in universe, but several Star Trek actors make guest appearances. The most blatant example is probably in "Graphic", where Wil Wheaton plays a comic book collector at a fan convention where multiple Star Trek costumes are seen.
  • Cell Phones Are Useless:
    • In one episode, Don tries to call another agent to warn her that there's an assassination plot in progress on the witness she's getting out of jail. He can't get through because there's no cell service inside. Justified in that there's a reason for a detention facility to intentionally jam cell phone reception within its walls; in the event that someone manages to smuggle in a phone despite their security procedures, this creates another line of defense to ensure that inmates wouldn't be able to use it.
    • In another episode, a kidnapping occurs and the agents only have one hour to save the kid (the episode takes place in a near-Real Time, as well) and could really use Don's help as team leader. Alas, the B plot of the episode is that Don is in a Bureau-mandated psych session courtesy of being involved in a shooting in a prior episode and the psychiatrist ordered Don to turn off the phone. Don only finds out something happened once he returns to the office in the episode's denouement. (In a later episode, the audience learns that Don's psychiatrist has learned of this incident and no longer makes him turn off his phone).
  • Central Theme: Using math to solve crimes.
  • Chained Heat: Downplayed in "Trust Metric". Colby and Dwayne escape from a prison transport van while they're being transferred between facilities, thanks in small part to a handcuff key that Colby smuggled along, but they lose the key before they can remove their leg cuffs, so they have to make their getaway still shackled together. They cut them off within a scene or two, and it ends up being a fairly minor detail.
  • Character Death: Dwayne Carter and Mason Lancer in the season four episode "Trust Metric".
    • Adam McKnight in the second episode.
    • Paul Stevens in the episode "Scorched" after he tries to escape from Don and his team after he is found out to be the arsonist.
  • Character Development: A very good amount of it, and not always in predictable directions (lookin' at you, Fleinhardt). Probably more so than most other Police Procedural shows.
  • Character Title:
    • Sniper Zero.
    • Charlie Don't Surf.
  • Chekhov's Classroom: A more subtle version plays out a few times, albeit it's usually Charlie teaching the lesson. In these cases, it's not a blatant case or learning something that he needs to know to help the case, but rather Charlie will be teaching a more abstract theory and then, with that thought fresh in his mind, later realizes that some element of that theory can be applied to whatever it is that he's having a hard time figuring out.
  • Chekhov's Gift: In "Checkmate", Don is reuniting with his Old Flame Robin while the latter is in FBI protective custody, and gives her a hairclip as a memento of their old relationship. Later in the episode, a Professional Killer is pursuing Robin, but Don uses a tracker hidden in the hairclip to catch up with them just in time.
  • Chekhov's Skill: The subplot of a Season 2 episode centers around Don and Charlie learning that their mother was a gifted musician, in the course of which it's revealed that Don and Charlie took piano lessons as children and while neither of them stuck with it long-term, Don apparently picked up and retained at least the basics as he's able to play the piano in The Tag. In the Season 3 finale, Don finds a key to help Charlie solve a Mad Bomber's puzzle when he realizes that a particular sequence used by the bomber is based on the G-major scale.
  • Child Prodigy: The backstory of Charlie is that he is a math child prodigy. When he was three, he was able to multiply four-digit numbers in his head.
  • Chuck Cunningham Syndrome:
    • Prosecutor Nadine Hodges shows up in several episodes and is set up as a possible love interest for Don, only to disappear in the middle of the season and never be so much as mentioned again.
    • Millie Finch doesn't appear after Season 3, although she's referenced once in Season 4.
  • *Click* Hello: Cold Sniper Ian Edgerton has done this to perps several times throughout the series.
  • Cloudcuckoolander: Larry Fleinhardt is this combined with Absent-Minded Professor - as he is a brilliant thinker with remarkable insight, but walks around with his head in the clouds and tends to let more mundane matters slip his mind.
    • For several seasons, he eats nothing but white food.
    • In one classic example, he makes a breakthrough in the case while in the hot tub and ends up running across campus in his bathrobe yelling about Archimedes. At the end of the scene, he finally realizes he's been separated from his clothing, and then has to try and remember where he left it.
    • In another episode, he's said to have called Amita from a conference in Minneapolis because he couldn't remember whether he was in St. Louis or Cleveland.
  • Cold-Blooded Torture:
    • In the Season 4 premiere, Mason Lancer tortures Colby by injecting him with drugs after The Reveal that Colby is a Fake Defector. The first impairs his breathing, creating "the sensation of slowly drowning", and the second massively increases his sensitivity to pain, among other effects. The torturer then attempts to kill Colby with a third drug, but Dwayne performs a Heroic Sacrifice to stop him before Colby gets a lethal dose. While the torture isn't particularly graphic, which makes the scene truly horrifying is the extent to which Mason is almost inhumanly calm and unbothered the entire time - he's not enjoying Colby's pain per se, but he's so completely indifferent to the suffering of another human being that it's almost worse.
    • A few episodes later, they get a killer who tortures his victims for days before killing them. The same episode reveals that Megan was forced to take part in "interrogations" of terrorism suspects, even though she was horrified by the idea. Allegedly this was a case of Enhanced Interrogation Techniques, but Megan, who knows that Torture Is Ineffective, sees this as this trope.
  • Cold Sniper: Agent Ian Edgerton.
  • Content Warnings: Season 5 Episode 8 "Thirty-Six Hours" deals with a train derailment. It was written and filmed before the tragic Metrolink crash in Chatsworth, CA but was shown after. David Krumholtz gives a content warning that establishes the episode was written and filmed before the tragedy and gives a warning so those who might find the story disturbing can make an informed decision.
  • Connect the Deaths: Practically every episode, but in one of the early episodes, Charlie develops an algorithm which, based on the inherent human inability to produce random numbers/circumstances, uses a map with pushpins to find where the next murder will/would have occurred.
  • Conspiracy Theorist:
    • One shows up in "Calculated Risk", intent on seeking the truth behind the financial collapse of a big company. He's enough of a paranoiac to disbelieve that the team are real FBI agents when they confront him.
    • Roy McGill (played by Josh Gad), is a specialist on conspiracy theories and an amateur police consultant, who assists the FBI on a couple of cases.
  • Continuity Nod: One episode mentioned a gang called the 18th Street Mexicali, a rival of the gang one of the suspects belonged to. Two episodes later, the gang is mentioned again as a gang that a record-label executive—and the father of the kid kidnapped in the episode—is connected to.
  • Contrived Coincidence:
    • In "Vector", the FBI is called in by the CDC to help investigate a viral outbreak (given the possibility that it may have been an act of bioterrorism). Don wants to bring Charlie, but the CDC insists on using their own mathematical consultant who has the proper clearance. Naturally, the CDC consultant turns out to be Charlie.
    • The case in "One Hour" is this to some extent. The team gets a case while Don's at a therapy session with his phone off, and it just happens to be one with an incredibly short deadline, so much so that the case is fully resolved and wrapped up by the time Don shows up, when many FBI cases require days if not weeks of investigation.
    • In Season 5 Episode 7, a family friend of the Eppes asks Don to look into his surfer son's death, ruled an accident. Don looks over the Park Ranger investigation into said accident at his desk and thinks the investigation was pretty thorough as Colby walks by and recognizes Don's Surfer friend. It is Colby, an Idaho farmboy, who realizes the death was murder because he just happens to be a hardcore surfing fan and notices a detail the park rangers missed.
  • Conveniently Unverifiable Cover Story: A situation-specific example occurs in one episode when Colby is posing as an arms dealer to sting a dealer. When he's asked how he got the dealer's name, he claims to have been referred by an associate of the dealers who had recently died, preventing the dealer from being able to verify (or, in this case, disprove) his story. It actually works. Unfortunately, the dealer catches on another way.
  • Cop and Scientist: Cop and mathematician, but otherwise fits the trope.
  • Couch Gag: Each episode opens with a grid-patterned screen, each quadrant of which displays the number of something—suspects, dollars, crimes per day, people, whatever—relevant to its plot.
  • Counterfeit Cash: "Counterfeit Reality" dealt with an artist kidnapped to help a counterfeiter gang.
  • Covert Distress Code: At the beginning of season 5, new girl Nikki goes undercover to catch a group of people kidnapping ATM users and is given the distress code "Mexico" to use if the operation starts to go south. It does, but she's too stubborn to use the word, believing that she can salvage the operation on her own. Don berates her for this later and assigns her to answering telephones.
    • "Mexico" is actually David and Colby's long-time covert distress code; each of them uses it once successfully (Colby in "Chinese Box", David in "Ultimatum") when the other is in a hostage situation, to warn each other that a hard entry is imminent.
  • CPR: Clean, Pretty, Reliable: Left ambiguous in "Trust Metric", when David Sinclair performs CPR on Colby Granger after Colby is injected with potassium chloride. While the "reliable" piece is shown to hold true, since Colby lives, the camera cuts away from the scene after only a few seconds, so the extent — or lack — of the "clean" and "pretty" aspects are left up to the viewer's imagination.
  • Crazy Enough to Work: Some people's reaction to the general premise of the series: an FBI agent working with his genius brother using Math of all things to solve crimes. Many of them come around to it by the end, with Don's Bureau mandated therapist actually telling him the reason he's the head of his own unit is because he's the type of person to do something so unconventional and make it work spectacularly.
  • Creator Cameo: In the Season 2 episode "Backscatter", two guys from the Russian mafia come and threaten Charlie by sitting in the back room while he's teaching. One of them is Nicolas Falacci, one of the creators of the show.
  • Crime After Crime:
    • The perpetrator of "Calculated Risk". Frustrated that his father isn't giving him respect at the family business, he embezzled around $300 million from the company, authored a scam to cover his tracks that possibly brought the whole company down, and then murdered the CFO when she started digging too deeply.
    • The mastermind of "End of Watch", a narcotics cop who took location tips of drug stash houses from one gang and fed them to another gangster from another gang so that he could raid them and get more drug dealers off the streets. When the raider wanted to come forward, he arranged for him to go down in a police raid. Then when the rookie cop that pulled the trigger got suspicious and decided to go to IA, the Dirty Cop killed him. And then when the rookie cop's murder case got hot again, he killed the original tipster when he started talking to the FBI.
  • Criminal Mind Games: The episode "The Janus List" has a character who, in essence, does this for its own sake. He knows he's dying and wants to hand off his life's work, the eponymous list, to Charlie, but only if Charlie is worthy of it. So he hides the information behind a series of complicated codes and puzzles, which are in essence a test; if Charlie is able to get through all of the layers to access the list, then he's passed the test and proven himself worthy. He does, although one of the pieces ends up being figured out by Don.
    • Lots of episodes do this to some extent, though not to the same degree as "The Janus List". Usually the clues require advanced mathematics to unravel, since the show's Aesop is that "Math is useful and mathematicians are like superheroes—with math."
  • The Cuckoolander Was Right: Larry is somewhat perpetually this. One doesn't get a PhD without having some intelligence. Somewhat subverted in that the team is aware of this and usually listens to him right off the bat (though it sometimes takes a little white for them to figure out what he's trying to tell them, since he doesn't always say it straight out).
    • Played with in "Calculated Risk". One of the suspects in the murder of a whistleblowing CFO is a former employee of her company, and he spends most of the interrogation going on an apparently inane rant about the company. They write him off as soon as his alibi clears, but then later, as more evidence surfaces:
      Megan: Did he say these people weren't real?
      Don: He said we would never find them. What, do you think he figured it out?
      Megan: I don't know, but he's right!
    • Played with in a later episode. A conspiracy theorist claims that a public figure and his charitable organization aren't on the up-and-up. He turns out to be right, but the implication is that it's pretty much luck and chance; given how many people he thinks are doing something illicit, one of them was bound to end up being actually sleazy. note  The trope is even Lampshaded by Robin.
      Robin: on the other hand, McGill may not be so crazy. (Beat) Okay, he's crazy, but that doesn't mean that he's wrong.
      • But played straight with the same character in a later episode, where he finds a clue that helps Charlie crack a serial killer case.
  • Cult Defector: CBI Agent Willons from the episode "Nine Wives" grew up in the cult at the center of the episode. She escaped at the age of nineteen when her cult-assigned husband died.
  • Culture Justifies Anything: The villain of "Trouble in Chinatown" tries to make this argument for ghost brides, but given he's trying to force the issue by murdering undocumented Chinese women workers to give dead Chinese bachelors wives in death, no-one buys his argument. The Chinese-American ICE agent with the team even pulls a Shut Up, Hannibal! by shouting "Shame on you!" at him.

    D-F 
  • Damn You, Muscle Memory!: In-Universe example in "Primacy", where the FBI try to nab a player who's after an in-game MacGuffin with an accompanying million-dollar cash prize, by creating a fake game server and letting him win the fake MacGuffin. The plan goes awry when Amita, who's played the game since university, accidentally kills the target's avatar and apparently wins the MacGuffin herself, making her a target.
  • Dark and Troubled Past: The brothers are mostly spared this (aside from losing their mom to cancer) but other characters are not so lucky.
    • Megan Reeves literally disappointed her father by being born female (she was his last chance to have a son), and she spent years trying to get his attention, first by positive means and then by acting out, until she finally ran away at 16.
    • David Sinclair grew up in a gang-ridden neighborhood, losing one of his best friends to gun violence when he was in high school, which another best friend was unjustly imprisoned for. He also says at one point that his father died when he was about 14.
    • Colby Granger lost his father in a single-car wreck when he was 15; the cause of the wreck was never determined, but Colby always suspected it might have been a suicide, as his father had recently lost his job and was devastated. And that's not even getting into his time in the military, where he saw way more than his share of trauma.
    • Liz Warner's early life is never discussed, but she does say at one point that she had been pregnant in college and miscarried, and that her friends were so insensitive to her about it that she never spoke to them again.
    • Nikki Bettancourt's past is also not really explored, but we do know that early in her career, she was dumped into undercover work unprepared and one of the targets tried to rape her. The way she plays it off as no big deal also suggests she might have more (ultimately unexplored) trauma in her past.
  • Dark Messiah: Nine Wives has Abner exploiting his followers' spiritual yearnings for his own gains, posing as a savior, when in reality, he is nothing but a sexual predator and abuser.
  • Dead Man Writing: "Undercurrents" has one from an Intrepid Reporter, who went undercover into the Chinese human trafficking trade to get an inside scoop, only to have her body wash up on the beach when she was dumped overboard. Charlie gets a voice message from her when he calls an encoded phone number tattooed on her foot.
  • Deadpan Snarker:
    • Colby can be this at times.
    • Megan Reeves is also this.
    • Nikki does this as well, with David being the usual target.
  • Dead Person Impersonation: In one episode, David thinks that Ron Allen, a supposed witness to burglary, isn't on the up-and-up, so he runs a deep background check and finds that the real Ron Allen died in infancy. They eventually discover that he'd been pulling this scam with different identities at different schools for years, stealing things from each school as he went along.
  • Decoy Damsel: One shows up in "Tabu". At first she appears to be kidnapped by an environmental gang as leverage against her businessman father, but then she starts shooting up the FBI with the gang and it's revealed that she co-opted the gang as part of a giant tantrum against her father.
  • Defensive Feint Trap: Used in the episode Assassin and discussed with a chess analogy.
  • Deliberate Injury Gambit: The climax of the pilot episode has Don holding the perp at gunpoint, except that he has David at knifepoint as a hostage. When the perp is suddenly distracted, David pulls the knife away to give Don a clear shot, even if it means gashing his wrist in the process.
  • Diplomatic Impunity: This is briefly suggested as something Chinese spy Dwayne Carter might try, but Sinclair points out that they have the consulate under surveillance; since Carter isn't a diplomat himself, he'd be fair game as long as they got him before he was inside. As it turns out, Carter plans to exploit international shipping laws instead.
  • Dirty Bomb: The episode "Dirty Bomb", where the FBI has to find a hijacked truck-load of radioactive cesium before it can be turned into one.
  • Disability Alibi:
    • In "Traffic", somebody is attacking drivers on the freeway with various weapons, which has resulted in several injuries and a few deaths. The FBI figures out that the culprit is someone who's received brain damage from a car accident that made it difficult for them to control their anger impulses, and they find one suspect that fit this profile. However, it turns out that the same accident that brain-damaged the suspect also left him with a non-functional hand and a barely-functional leg (either as a further result of the brain damage or from other injuries he sustained), meaning that he's not physically capable of using any of the weapons involved in the attacks. That, combined with finding no weapon evidence at his house, exonerates him of any suspicion.
    • In "Scan Man", the titular Idiot Savant is initially considered to be a suspect until the FBI actually meet him, huddled under a table watching an indy race on a portable TV and humming along to the cars.
  • Disappeared Dad: In "Calculated Risk", it is mentioned that Daniel's father is not in the picture and he has to go live with his grandmother after his mother is murdered.
  • Disposable Sex Worker: Inverted in one episode. The killer was targeting various prostitutes' clients because she was the sister of a prostitute who was beaten (and died due to being a hemophiliac).
  • Disproportionate Retribution:
    • "Sabotage": A disgruntled railroad employee/train crash survivor causes multiple fatal train wrecks to "get back at" the railroad for letting 36 people die and scapegoating him for the crash. The additional innocent people killed by his "demonstrations" don't seem to bother him.
    • One of the copycat victims in "Sniper Zero" is mentioned to have been killed because he didn't return the lawnmower he borrowed from his neighbor.
    • "Judgment Call": A judge's wife is killed by the widow of a murdered cop because the judge didn't give the cop's murderer the death sentence the widow wanted.
    • Subverted in "Soft Target": A former army major appears to have planted a bomb on a Homeland Security official who he blames for inadequate security measures that allowed several of his men to be killed in a terrorist attack. However, it's revealed that the bomb is actually a fake; he just wanted to make a point.
    • In "The OG": The kindly rec center owner who set off more than a half-dozen "chain reaction" gang shootings after a stray bullet killed his son, resulting in the deaths of hundreds of people, including innocent bystanders and children. Unsurprisingly, he's Driven to Suicide.
    • In "Backscatter": A Russian mob boss kills people over identity theft and insurance scams as a matter of policy.
    • "Traffic": A hit-and-run victim starts killing people associated with other accidents. It's implied it's not completely his fault that things are so out of proportion, as he suffered a several frontal lobe injury in his accident and has diminished impulse control.
    • "Devil Girl": A prostitute is murdered by a john, and her sister responds by targeting and murdering johns at random, whether or not they ever hurt the prostitutes. This later expands to killing a man who insults a prostitute and trying to kill a social worker (who was also trying to help the prostitutes) just for thinking he can do a better job than she can.
    • "Guilt Trip": An arms dealer kills his girlfriend on the suspicion that she's an FBI informant.
  • Distinction Without a Difference: After Nikki screws up on an assignment, Don assigns her to the telephones as punishment and she asks David how long she'll be in hot water for. David says that pre-therapy Don would've kept her there for 3 months, post-therapy Don should keep her there for 10-11 weeks.
  • The Dog Was the Mastermind:
    • In "Structural Corruption", the mastermind behind the defective building cover-up turns out to be the building owner's secretary, who he was having an affair with. She shortchanged her boss by hiring cheaper, substandard labor and pocketing the difference, because he wouldn't divorce his wife for her.
    • In "Calculated Risk", the killer and perpetrator of the scam that brought the energy company Syntel down is the CEO's son, who embezzled money from the company because he thought his father was snubbing him by giving him a desk job, and then authored the scam to cover his tracks.
    • In "Sacrifice", the killer is Scott, the victim's assistant, who was horrified enough at the implications of his boss's research to kill him.
    • In "Where Credit's Due", the killer (and original author of the script for a premiering movie) is the first victim's assistant and housesitter, Tyson.
  • Do Not Call Me "Paul": Recurring character Dr. Mildred Finch, who only wants to be called "Millie". She does not at all like the name "Mildred" (She tries to explain why once, but she's drunk at the time and can't stay on topic long enough to make sense), and she doesn't like to use her professional title either, at least not with people she sees on a regular basis.
  • Double Reverse Quadruple Agent: In "The Janus List", Ashby is said to have been this.
    Colby: By the time MI-6 cut him loose, nobody knew which side he was playing for.
    • Colby edges into this too in "Trust Metric". There comes a point when Don, Megan, and David can't even agree with each other about who Colby is and what he's up to. They do figure it out eventually.
  • Dramatic Drop:
    • In an early episode, Charlie is making a sandwich when he sees a news report on TV saying that FBI Agents are in a firefight with bank robbers; we see the knife he was holding drop to the counter as Charlie realizes that his brother Don is among the agents on the scene.
  • Dramatic Irony: About half of the episode "Trust Metric" is this, pretty much from the point when Colby first contacts Don. Colby tells Don that his "defection" is a cover and he's still working for the FBI, and he tells Don two people he can check it out with: Agent Michael Kirkland and the ranking guard on the prison transport he escaped from. The audience already saw Colby talking with a man who is later established to be Kirkland, and from their conversation that the ranking guard was in on it. But when Don tries to check out Colby's story, Kirkland is dead and the guard, suspecting a trick, insists he had nothing to do with the escape. Viewers know Colby is telling the truthnote  but the FBI team does not.
  • Duck Season, Rabbit Season: One episode uses a simpler version of this trope, skipping right to the switch without arguing. One of the characters even proceeds to compare it to Looney Tunes.
  • Early-Installment Weirdness: In the pilot, the viewer's first introduction to Alan is him playing with a pet bird in a cage. The bird disappears by the second episode, with a fish tank ultimately appearing in its place.
  • Eco-Terrorist: In the episode "Scorched", the team is investigating a series of arson cases, which have the name "ELM" being found a the scene. The group insists that they are not involved with the arson and accuse the FBI of trying to frame them for the fires. It later turns out to be a fire investigator setting fires, with him using a friend of one of the activists, who is a prodigy who wants to fit in.
  • Education Mama: Subverted with Alan and Margaret. Even though they had Charlie who was a clear Child Prodigy, they worked hard to ensure they were giving him what he needed rather than pressuring him to perform to an external standard.
  • E = MC Hammer: Averted. The network actually hired professors to teach Krumholtz the real math he needed to know.
  • Embarrassing Nickname: Don occasionally likes to tease Charlie by calling him "Chuck", to Charlie's annoyance.
  • Empty Cop Threat: Not every episode, but on occasion.
    • Referenced in the first episode of season 2, where ex-military New Meat Colby tries to intimidate an entire gang and it falls to David to defuse the situation. David chastises Colby later for "selling wolf tickets".
    • In the episode "Toxic", a private security contractor was found going through the files of a journalist the FBI was visiting. After confirming his credentials, and after the journalist declined to press charges, Sinclair let the contractor off with a warning that if they ever caught him near their investigation again, he would charge him with obstruction of justice personally. The contractor later shows up about to snipe a witness to their case, but Edgerton gets the drop on him before he can — after which criminal charges are a moot point.
    • Another episode uses the trope: A man hires private security to find his stolen loot. The FBI is also on the case as two people were kidnapped during the theft. The private security guys barge in as the FBI is about to arrest the kidnappers, which allows them to escape. Don immediately has both men arrested as an accessory to the kidnappers, and warns their employer that if he sees any more of his employees following FBI agents around, he'll have him arrested under the same charges.
  • Enhance Button: A first season episode deconstructs this trope. They are able to "zoom in" on a poor-resolution image, but Charlie and Amita explain that what they're seeing isn't actually information contained in the original image (and in fact, Amita initially enlarges the image to show that that alone doesn't do any good), but rather a predictive tool that extrapolates from the existing data to fill in the missing information as best it can.
  • Enhanced Interrogation Techniques: Megan is forced to temporarily leave the team and take a "special assignment" despite attempting to decline, and seems subdued and out of sorts upon her return. She eventually admits (after Colby guesses as much) that her assignment involved advising on these sorts of interrogations. Her horror and disgust at this are a major factor in her decision to quit the FBI a season later.
  • Entitled Bastard: One shows up in "Money For Nothing", as an investor who bought a large amount of Zambian debt for pennies on the dollar demands that the relief money should be given to him and even hires private security to track it down after it's stolen, resulting in at least one missed opportunity for the FBI because the private security guys get in the way. He changes his mind in the end and agrees to settle for the (much lower) amount that he paid to buy the debt rather than continue to demand payment in full.
  • Epic Fail:
    • One episode has a suspect flee from the Feds in the middle of his shower, and tries to carjack two women. By the time David and Colby catch up, the women are kicking the crap out of him.
    • In the episode featuring the hacker on the run from various criminal groups, the Israeli hacker/arms-dealer gets cornered by an FBI agent while said Israeli hacker's muscle is elsewhere. The hacker makes a break for the glass window—but does not expect for the break to fail so spectacularly, as the hacker's body (appropriate for his specialty, and thus not made like a linebacker's) bounces off the window not once, not twice, but three times. He is caught, obviously, no doubt wondering why the breakaway glass didn't break away, like in the movies.
  • Et Tu, Brute?:
    • The team is visibly crushed when Colby is revealed to be a double agent for the Chinese, especially David. After things are cleared up, their relationship is rocky for several episodes before they finally get it together again.
    • Lieutenant Walker is furious when he learns that one of his fellow cops, a narcotics officer, was so intent on clearing the streets of drug dealers that he secretly collaborated with a gang member to clear rival stash houses, organized the gang member to go down in a raid when he wanted to come forward, and even killed the officer that pulled the trigger when he got suspicious and decided to go to Internal Affairs. Especially since he helped raise his murdered colleague's son afterward.
    • Don takes it hard when he finds out that his FBI mentor turned out to be a Dirty Cop, especially when he had to shoot him.
  • "Eureka!" Moment: Charlie, all the time, mostly highlighted by scenes of mathematical analogies and formulas flickering past his eyes.
    • Amita does it while Charlie is otherwise occupied in "Checkmate", leaving a bemused Larry to wonder, "What is it about this office?"
    • Larry gets one too, in "All's Fair". It being Larry, it's a somewhat literal interpretation.
    • Don gets one in "The Janus List"; Charlie, who's not used to being on that side of it, is both amazed and somewhat taken aback.
      Charlie: Is that the face I make when I...?
  • Everybody Hates Mathematics: Played with, inverted, and subverted. Several characters, including lead Charlie Eppes, love math, and those who don't love math are dependent on those who do.
    • Hell, by the fifth and sixth seasons, some of the FBI actually explain the math, with Charlie grinning like a proud teacher.
  • Everybody Lives: Has a few in the later seasons:
    • "Chinese Box" has only an attempted murder; the intended victim gets a few non-lethal gunshot wounds.
    • In "Power", the team is chasing a serial rapist rather than a killer.
    • "Jacked" has a particularly clever variation: the FBI witnesses an apparent murder via hidden camera, but it turns out to be staged.
    • Similarly, in "Hydra", a non-custodial mother claims to have killed her daughter as the cops were closing in. She eventually admits that she was lying: her daughter was actually a clone, and her "father", the custodial parent, treated her as nothing more than a scientific specimen, so the mother tried to fake the girl's death so the police and the researchers would stop looking for the child, giving her a chance to disappear into a normal life.
  • Evil Cannot Comprehend Good: The episode "End Game" centers around Ryan Ferraro, a disgraced former Army captain, trying to set a trap for Clay Porter, the soldier who blew the whistle on him for torturing a POW to death, believing that the POW must have blabbed the secret to Porter before his death. It turns out that Porter knew nothing about the secret, nor did he give Ferraro any real reason to think he did - except that he turned Ferraro in, and Ferraro simply couldn't comprehend any reason why Porter would do that other than Porter having something to gain by Ferraro's going to jail. It never occurs to him that Porter might have simply had a conscience.
  • Evil Counterpart: Quite a few episodes had the criminal being a genius Charlie could relate to. Subverted with Dr. Glazer in "Burn Rate", as he turns out to be innocent.
  • Evil Parents Want Good Kids: A variant occurs in "One Hour", the Victim of the Week's father fit this trope to a tee, except that his Heel–Face Turn predated his son's birth. As far as the son knew, his dad was just the owner of a record company. So when the son was kidnapped by one of dad's old associates who wanted a piece of the dad's company, the dad, Che Lobo, was understandably distraught, because he made a vow to himself that he'd never let the unsavory part of his past affect his son, because he wanted his son to have a chance to be "something better".
  • Exactly What It Says on the Tin: Zig-zagged with Charlie's book. The title he uses when he submits it is "A Mathematical Analysis of Friendship Dynamics", which is exactly what it sounds like. However, when it gets published as a mainstream book, the publisher convinces him to change the title to something more catchy, which ends up being a bit less precise.
  • Expy: Bill Nye. Played by Bill Nye.
    • Another example would be the villain of the Season 5 finale: a very intelligent cult leader who has a bit of a god complex and whose followers are only women. He's played by James Callis. There are few differences.
  • Explain, Explain... Oh, Crap!: The deduction of motive in the episode "Dreamland". After finding out a company's project was going awry due to the R&D process not going fast enough, Charlie asks his CalSci engineering colleague "Otto-bahn" if he thinks he could complete the project in two weeks given the funding. Otto-bahn eagerly agrees that it's possible if they got enough manpower and took some risks, before realizing that that exact mindset was what led the company's people to volunteer themselves as test subjects and got them killed.
  • Exposition Diagram: The show uses this Once an Episode, in the form of an Imagine Spot of whatever analogy Charlie (or occasionally Larry or Amita) is using for his math, overlaid with some relevant (or at least relevant-looking) equations and graphs and stuff.
  • Expository Hairstyle Change: In the Season four premiere had several characters grow facial hair or at least a significant amount of stubble. Colby at least had the excuse of having been in jail, but it was like the "Everyone Grows a Beard" episode. Colby and Charlie shave by the next episode, but Larry keeps the stubble.
  • Explosive Stupidity:
    • The arsonist villain of "Scorched" tries to hold off the FBI with a container of white phosphorus. He bangs his head while trying to escape through a pipe and drops the container, incinerating him alive.
    • David and Colby corner a shotgun-wielding suspect in a garage that was recently used to make bombs, and the suspect firing his weapon causes the residue to explode and kill him. However, he clearly did recognize the danger posed by explosive residue in the air (the earlier parts of the episode had him getting his associates to smoke outside), so his mistake is more likely the result of panic, or it might even have been an intentional Suicide Attack.
  • External Combustion: Takes out potential witnesses in "Democracy" and "Pay to Play"; another almost gets killed in "Blowback," but the bomb goes off too soon.
  • Extreme Graphical Representation: Justified in one episode, where a computer scientist hides the fact that his artificial intelligence computer is a fraud by creating a very elaborate and impressive-looking computer room and interface.
  • Extremely Protective Child: Joel, the grandson of Holocaust survivor Erika Hellman, is incredibly protective of his grandmother, especially when it comes to her quest to win back the Pissaro painting that had belonged to her father before the Nazis stole it when they sent them to the death camps.
  • Extremely Short Timespan: Most episodes takes place over the course of days if not weeks, but there are a few exceptions.
    • "One Hour" is probably the shortest. While it doesn't literally cover only an hour, the first scene takes place in the early morning and the episode wraps up before lunch. It's short enough that Don misses the entire thing because he's at a therapy appointment.
    • Between the lack of night scenes and the timeline of events, "Trust Metric" (with the exception of the opening scenes) appears to take place over a single day, though this is never made explicit.
    • "Jacked" is set around a four-hour bus hostage crisis.
  • Facepalm: Charlie did this once when Larry said that perhaps the suspect could be in two places at the same time. (It was a quantum idea).
  • Failed a Spot Check: The villain of "Primacy". For all that he divines about Amita (whom he's targeting for winning a MacGuffin in an online game), including her name, address, workplace, etc., he somehow fails to notice that she often works closely with the FBI, and is thus taken off guard when his kidnapping attempt turns into an FBI trap for him.
  • Fakeout Escape: One episode features a variant of this, where a prisoner fakes escaping for the benefit of The Cartel (who are trying to have him killed in prison before he can turn informer) rather than the guards. He makes a deal to switch ID numbers and tracking bracelets with another prisoner who is about to escape so that the cartel will look for him outside the jail. He then switches places with yet another prisoner for $1,000 so that if the cartel figures out the deception, they'll look for him in the wrong part of the prison.
  • Fakin' MacGuffin:
    • Where the MacGuffin in question is a math equation. A mathematician's daughter is kidnapped to get him to turn his ground-breaking solution to the Riemann hypotheis into a codebreaking tool. When Charlie finds out that his solution will not work, Don comes up with the idea of giving them a fake solution that will open an electronic door that the FBI would set up for them, which would allow them to track down their location, raid it, arrest the criminals, and save the girl.
  • Fake Defector: Colby Granger turns out to have been a triple agent for several years. This causes a fair bit of drama and angst, since the rest of the cast find out about the "defector" part well before they find out about the "fake".
  • Faked Kidnapping:
    • "Magic Show" involves a magician with a record of faking disappearances in her act and even specifically inviting law enforcement officers to her show to drum up publicity after she disappears "for real" onstage. Then it all goes awry when her equipment malfunctions and she is killed by her trick.
  • False Cause: In one episode, Charlie tells Don about the ice cream-rape correlation. As the sales of ice cream goes up, so do the number of rapes. The key is both take place during the summer.
  • False Confession: One episode involved Don finding out that he arrested the wrong guy for a murder the previous year. The suspect didn't realize how weak the case against him actually was (to be fair, neither did Don), so he confessed and took a plea bargain so he'd at least have a shot at parole rather than go to trial and be locked up for life if found guilty. Don gets the conviction overturned and the innocent man released as soon as they catch the real killer.
  • Famed In-Story: Charlie is this already by the time of the beginning of the series, well known for his genius and publishing several papers before he was 18. In an early season 1 episode, an investigator for the TSA actually recognizes and fanboys a little over meeting him. As the series progresses, he and Don become well-known among the FBI and other federal agencies for their unorthodox methods; a couple episodes had agents specifically requests Don's team to utilize their skills and Charlie's talents.
  • Family Relationship Switcheroo: an episode revolved around a polygamist cult features a pair of women who are sisters and mother and daughter (unknown to the daughter until some way into the episode).
  • Fatal Family Photo:
    • "Burn Rate" starts with a Fatal Family Montage; the initial Victim of the Week is seen enjoying a moment with his wife, son and daughter before heading to work. When he receives a letter bomb, the debris is seen raining on a family photo.
    • "Scan Man" starts with an FBI arrest gone bad and one of the agents gunned down. His last moments were him reaching for his fallen helmet, in which was a picture of his family.
  • Fatal Method Acting: In-Universe example in "7 Men Out", one suspect in the case of the week is a man who had been the producer of an extreme stunts reality show called "Thrill Drill", which was cancelled after a stunt gone wrong resulted in a contestant being decapitated. (The producer had lost nearly all of his money and assets in the ensuing legal process, leading the agents to suspect - correctly, as it turns out - that he got involved with the scheme they're investigating in an attempt to regain some of his previous wealth).
  • FBI Agent: Half the main cast is one. For the whole series, Special Agents Don Eppes and David Sinclair. For some seasons, Special Agents Terri Lake (Season 1), Colby Granger (Seasons 2-6) Megan Reeves (Seasons 2-4), Liz Warner (3-6) and Nikki Betancourt (5-6), plus frequent guest star Ian Edgerton.
  • Feed the Mole: The strategy used in the episode "Assassin".
    • This was also part of Colby's mole operation. Under the guidance of his handler, Colby fed information to genuine mole Carter in the hopes that Carter would eventually reveal the identity of his contact. He does. Unfortunately, it's not until after said contact had figured out Colby's true allegiances.
  • Fictional Counterpart: CalSci is basically Caltech in everything but name - right down to the full names (California Institute of Science vs California Institute of Technology), and the location (somewhere in Pasadena). Not surprising, considering several of the show's consultants are Caltech faculty, and some of the show has been filmed there.
  • Fictional Document: The book "Dreaming of Sean" that Alan was holding in his hands in "The Fifth Man" when Don regains consciousness.
  • Fictional Video Game: The online RPG Primacy in the episode of the same name.
  • Finally Found the Body:
    • In "End of Watch", a detective's body is finally found after being missing for 17 years and Walker is angry when he discovers that one of his own men was in on it.
    • In "The Art of Reckoning", the body of a congressman's young son is uncovered after the hitman who killed him finally points to the location where the boy was killed.
  • Finding Judas: In the first season episode "Vector", the team is investigating several deaths caused by a disease thought to be wiped out. In the end, the culprit ends up being one of the scientists responsible for looking after the remaining strains of the virus. He thinks that another outbreak was inevitable, and by infecting a few people, it would force doctors to find a cure and prevent an epidemic in the future. In fact, the finds him lighting candles at a church to pay respect to the victims.
  • Fingerprinting Air: Subverted in one episode. They have two potential suspects and a partial print. Charlie is critizing the forensic technician's methods- how does she know which finger it's from, etc.- and she gets pissed off at him and points out that the print has a rare marking that only matches one of the suspects. Then it turns out that the culprit was a third man, who had the same rare marking on one of his fingers.
  • Finger-Twitching Revival: Happens in "The Fifth Man", Don is unconscious for much of the episode after being stabbed in the chest. A sleeping Alan's hand is next to his son's and Don's fingers start moving, which wakes Alan up to see Don has regained consciousness, who spends the next episode recovering from his injury.
  • First Girl Wins: Happens for both the Eppes brothers.
    • Right from the beginning of the series, Amita hangs around a lot more and works a lot more closely with Charlie than any other grad student, prompting both Don and Alan to comment on the potential there. After two seasons of Will They or Won't They?, they get together in the beginning of Season 3 and stay together for the rest of the series, marrying in the series finale.
    • Though a couple of female characters are mentioned to be ex-girlfriends of Don's, the first woman that he's actually seen involved with is Robin Brooks. Though they break up six months later (her decision, not his, which is significant in and of itself), they end up getting back together after working a case together, and she accepts his proposal in the series finale. Even Liz Warner admits that she knew she was just the rebound and that Don still loved Robin.
  • First-Person Perspective: In later seasons the show used gun barrel perspective as the FBI agents performed operations intercut with more regular footage.
  • Five-Second Foreshadowing: In "Scan Man", David and Charlie are bringing an Idiot Savant back home where he might feel comfortable enough to talk, but when they reach his apartment, he starts whining that his floor mat has big footprints on it and only small feet are allowed. David realizes that someone else is there seconds before the bullets start flying.
  • Fixing the Game: More than a few episodes involve games that prove to be influenced by external, illegal forces. Examples include horse racing in "Longshot", MMA match rankings in "Contender" and even Russian Roulette in "7 Men Out".
  • Flash Mob Cover Up: In the episode "Animal Rites", the villain organized a flashmob ahead of time to distract the FBI team at a key moment.
  • Foreshadowing: Before Colby was revealed to be a Chinese spy:
    Just the two?
    Just the two. Only one we need alive is the reporter.
    • The previous episode, "Money For Nothing", also contains a conversation between Don and Colby about loyalty that's rather prophetic.
      Don: How well does anyone know who they're working with?
      Colby: The way I see it, you got a team, you got to trust 'em. That's just the way it works.
    • Larry remarks in "Sniper Zero" that if he ever got a chance to go to outer space he wouldn't hesitate at the opportunity. In season three, guess what he gets to do.
  • Former Friends Photo: Colby is shown to keep several pictures in his desk from his days in the army. Among them is a picture of him and Dwayne Carter before Carter turned traitor.
  • Former Teen Rebel:
    • Alan used to be a member of a radical anti-war student group in the 1960's, which causes friction when Don ends up investigating a bombing that ends up linked to the group. The culprit is the son of another ex-member, who turned more conservative after the war ended.
    • Megan revealed that she was a bit wild when she was younger, eventually running away from home when she was 16 due to having problems with her father, as she was his last chance to have a son.
  • Found the Killer, Lost the Murderer: In one episode, a hidden camera catches an image of the man responsible for planting a bomb in a meeting, and another witness recognizes him and gives them a name. The man in question is killed in a shootout with the FBI, and when they search his apartment, they find a check dated just before the bombing. They realize someone paid him off to do it, and with the bomber dead, they don't have any leads. Luckily, Charlie comes up with something.
  • Fresh Clue: Whenever Ian Edgerton shoes up, he does two things: track the bad guys using Fresh Clues, and kill them from afar when necessary. In his second appearance, he establishes his credentials by finding the remains of a sandwich and identifying it as being less than a few hours old.
    Ian: She didn't like her PB&J. The ants haven't found it yet.
  • Friendly Local Chinatown: Using Los Angeles' real Chinatown in the fifth season episode "Trouble in Chinatown".
  • Friendly Enemy: Charlie Eppes and Marshall Penfield in the fifth season story "Frienemies".
  • Friendly Sniper: Agent Ian Edgerton oscilates between a mild version of this and Cold Sniper depending on the episode. It might be done purposely, since it is known he likes messing with people's heads. Especially Charlie and the team's.
  • Friend or Foe?: In "Rampage", Colby tells David that he was involved in an incident of this type when he was in Afghanistan.
    Colby: The Northern Alliance was already in Kandahar. The Taliban was running this rear guard action of the Shahi-Kot Mountains. There were just caves and bunkers everywhere. Seemed like every night these guys would come out and just pound us with RPGs. So, finally, one night, we decided to cut them off and set up an ambush in between the base camp and the pass where they would go up into the mountains. Only later we realized that SAS was already up there working that area. By the time they put together our ambush with their call for help, there were already two British soldiers dead.
  • Friendship Moment: Happens occasionally, usually among the FBI team members.
    • A particularly striking one in "Thirteen", when David is still keeping Colby at arm's length for the most part. Colby tries a spectacularly dangerous stunt to catch a suspect, which ends with him falling off a moving truck and hitting the ground hard. David runs to his side to help him up and inquire if he's okay.
    • Also during this arc, if the viewer watches carefully, every time David pushes Colby away, Megan is right there to check up on him and make sure he knows that someone still cares about him.
    • David has a moment of this with one of his childhood friends in "Contenders". David and his friend spend most of the episode verbally sparring, but at the very end, once they've sorted out their differences, David hugs his friend and calls him "brother".
  • Fun T-Shirt: Charlie is frequently wearing geeky shirts, including one with the pi symbol made up with the digits of pi.

    G-I 
  • Gambit Roulette: This is a common problem in that it relies on mathematics far more than real investigations ever would. While statistical analysis and some other techniques are used in law enforcement, they are not used in individual cases to the same degree as in the show. For example, an episode centers around a dirty bomb threat somewhere in LA, which turns out to be fake; the actual point of the threat was to trigger the evacuation of the immediate area, so the crooks could break into a vault without interference. However, the plan requires that the FBI evacuate the right area, which was not revealed by the "terrorists" and which is only determined at the last minute through extreme deductive skill (and nearly incorrectly anyway). Had the FBI guessed wrong, the plan would have failed.
  • Gambler's Fallacy: Invoked in the pilot, when Don, watching a baseball game with his father, comments that a batter is "due" a big play after going four games without a hit. Charlie is quick to refute this theory, saying that there's "no statistical evidence for a batter being 'due'," but the player does in fact get a big hit. However, it's quickly revealed (to everyone but Charlie himself) that Don is just messing with his brother; what they're watching is not a live game but a tape of a game from the day before, and Don, having read a recap in the paper, already knew what was going to happen, knew that Charlie would react to the fallacy, and intentionally set the whole thing up just to yank Charlie's chain.
  • The Gambling Addict:
    • In the episode "Bettor or Worse", it's revealed that the victim whose wife and daughter were kidnapped is one, and he arranged the kidnapping of his family and the robbing of his own jewelry store to get the insurance to pay off his gambling debts.
    • The episode "Double Down" reveals that Larry was once one, and although he got out of the habit, one of his fellows wasn't as lucky. Said fellow got some of his students into the card-counting realm of cheating casinos, and the situation ended with two of them dead and another one in jail. Larry is disgusted at what his old friend got his students into.
  • Game of Nerds:
    • Dr. Fleinhardt is a Dodgers fan.
    • There is also another nerdy character that plays Fantasy Baseball, Oswald Kittner, who's played by Jay Baruchel, who is a real-life friend of David Krumholtz, according to the DVD commentary on that episode.
    • Don was also an accomplished player, although not quite good enough for the pros, before joining the FBI. Charlie also played Little League at one point but wasn't quite as good as his brother.
    • Charlie is also somewhat implied to be a fan, as he calls it "the most statistically driven sport in the world" with a note of pride in "Sacrifice" note  and chuckles in agreement when Alan jokes that you don't need statistics to predict that The Dodgers aren't going to win the pennant that year.
  • Gangsta Style: One episode showed two gangsters firing their guns this way. They missed.
  • Geeky Turn-On: Charlie is trying to break a code for one of his FBI cases, but he's only gotten halfway. Amita looks it over and tells him the solution to the second half. Charlie just stares at her for a moment before blurting out, "Do you want to go out sometime?".
  • Genius Book Club: Charlie is shown packing a copy of Seven Pillars of Wisdom to read while teaching at Cambridge.
  • Geniuses Have Multiple PhDs: Charles is an incredibly brilliant mathematician who published his first treatise as a teenager and has only gone up from there. "Decoy Effect" mentions he is a multiple PhD.
  • Genocide Survivor: An elderly Jewish-Holocaust survivor named Erika Hellman is a one-shot character in "Provenance".
  • Gentleman and a Scholar: Charlie and Larry in different ways. Amita, too.
  • The Ghost:
    • Dr. Laurel Wilson in "Sabotage", a friend-turned potential girlfriend of Larry's, as she is mentioned but never made an appearance and Larry later starts dating Megan Reeves.
    • Irene, Margaret's aunt and is said to have a troubled relationship with Alan, is also mentioned but never makes an appearance.
  • Give Geeks a Chance: Charlie and Amita. It's true she's a computer geek, but she's a smoking hot computer geek.
  • Good Parents: Alan.
    • Margaret Eppes, too, judging by the way the entire surviving Eppes clan talks about her.
  • Good with Numbers: Charlie, of course.
  • Gracefully Demoted: In Don's backstory, he was the Special Agent in Charge of the FBI Field Office in Albuquerque but took a demotion when his mother got sick from cancer so he could transfer to the LA office to be nearby her and his other family.
  • Grade Skipper: Charlie and Don graduated from high school on the same day, despite the fact that Don is five years older than Charlie. This is particularly egregious because, even apart from the extreme unlikelihood of a child skipping five grades, Charlie was only a Child Prodigy in math and there's no indication he was advanced at all in other subjects, so while he would have had no trouble keeping up in high school math and might have been able to handle some of the sciences (particularly math=based science like physics), that grade level would have put him way out of his depth in the rest of his classes, but the show only ever talks about him having social, not academic, problems from being in high school at such a young age. (Although this could explain why his spelling is so bad).
  • Guns Do Not Work That Way: Fictional BNT-35 automatic rifle is presented as one of a kind high-caliber weapon that somehow use cartridges, that have no markings and absolutely unknown to experts.
    • Said rounds are somehow capable to perfecly maintain shape, stability and velocity even after penetrating thick brick wall.
    • However, FBI agents seems to be astonished that said rounds are capable to perforate both sides of a car body - something, that common .308 battle rifle would do.
    • There is a reason why most of the automatic rifles and machineguns have cyclic rate of fire about 600-800 rounds per minute (to ensure balance between controlability, volume of fire and ammo consumption). Nobody will design a military rifle with rate of fire of anti-aircraft gun.
    • Overheating causes barrels to warp, blow up and causes misfires and jams. However, violent chamber explosion that can kill the shooter more often would be caused by cartridge-related malfunction.
    • Even then, in order to overheat even the light thin barrel one would shoot more than a hundred of rounds in less than a minute - and even soldiers sometimes carry less ammo.
  • Hair-Trigger Explosive: Subverted. The perpetrator of "Protest" tries to hold off the FBI with a stick full of blasting gel, known to be much more powerful than dynamite, but Colby tackles him because he knows that blasting gel is also more stable and won't go off from simply being dropped.
  • He Had a Name: The third episode had a rare example of the perpetrator remembering the names of all his victims, who died as the result of a virus he unleashed with the endgame of trying to save many more lives. He was on his way to light candles for them in a church when he was caught.
  • He Knows Too Much:
    • In the episode "Democracy", five people who had evidence of a voting fraud conspiracy "accidentally" die before they can reveal the fraud. Unfortunately for the conspiracy, one of them managed to get the list of their names to Charlie shortly before being killed, who determines that the odds of five random people on a list dying in a given two-week period are approximately a bajillion to one. Don orders a second autopsy on the one who gave Charlie the list, which confirms that she was murdered, and the attempt to tie up a few loose ends has now attracted the attention of the FBI.
    • In "Disturbed", the episode after the credits opens with a murdered mailman who was last seen alive outside of a home where a woman was killed. He waves at the repairman entering the house. The repairman was a serial killer and he kills both his intended victim in the house and the mailman who could place him there. Nearly an aversion, since the mailman only possibly knew something.
      • The killer is stated to do this to pretty much anyone who comes even remotely close to being able to identify him. Unfortunately for him, one of his early attempts at this wasn't quite successful, and that witness ends up becoming the key to taking the killer down.
  • Heroic BSoD:
    • Charlie goes through a lot of these.
      • He goes through one in the very second episode "Uncertainty Principle" when Don is placed in a life-threatening situation because he followed Charlie's advice. He tries to work himself into a safe space by trying to solve the famously difficult P vs. NP problem. Don isn't happy about this since Charlie buried himself in the exact same problem after their mother got cancer, and it takes a while to coax him out of it.
        Charlie: [frantically] The fact that you survived is an anomaly and is unlikely to be the result of another such encounter.
      • He gets another one in "Rampage" due to the trauma from the shooting attack at the FBI (especially since he almost got caught in the crossfire), to the point where he refuses to go back there for a few days afterward.
      • He goes into worse ones in Season Five when Don is stabbed and nearly dies and three episodes later when Amita is kidnapped because a terrorist wants to use her for her computer skills. Luckily in both this cases, he's able to function by concentrating on using his math skills to help solve the case.
      • In the former case of Don's stabbing, Charlie actually works though the aftermath in the next episode by studying crime stats leading him to find a Serial Killer operating for over three decades that no-one even realized to look for.
    • It seems to run in the family. Don is prone to getting stuck in his own head when a case hits too close to home ("Trust Metric", "Arrow of Time", "Angels and Devils"). Not to mention arranging for Edgerton to beat up a suspect in the Season 3 opener.
      • In an earlier episode, "Rampage", Don had admitted to Charlie that he's able to cope while the situation is active, but runs into trouble when it slows down enough for him to think.
    • The mathematician in "Prime Suspect" has one when his solution to Riemann's hypothesis, which his daughter was kidnapped for, turns out to have a critical flaw that renders it incorrect, and thus worthless to trade for his daughter's life. Fortunately, Don comes up with another plan.
    • Also in "Rampage", Colby takes it pretty hard when it turns out that his bullet was what killed the suspected pedophile during the shooting attack, even after all of the evidence shows that it was an accidental death because the bullet that Colby shot through the attacker's shoulder to stop his rampage accidentally landed in the suspect's head so it wouldn't threaten his job at the FBI. Mainly because it reminded him of a similar incident during his Army days when his troop attacked a British troop mistaking them for Afghan enemies, which resulted in two British soldiers dying.
  • Heroic Sacrifice: Probably the only selfless thing Dwayne Carter ever does is to give up his life to save Colby. Doubles as a case of Redemption Equals Death.
  • Hero of Another Story: Though he is usually part of the main story, Larry takes a trip into space in Season 3 and spends several months living in the desert in season 6. He never gives more than very fleeting details about those experiences, but they would no doubt be interesting stories in their own right.
    • Megan also goes on special assignment for the latter half of season three (a case of Real Life Writes the Plot, as actress Diane Farr was pregnant). Becomes a bit of a subversion in that she seems to have come away from that feeling that she was more of a villain than a hero during that time.
  • He's Back!: In the Season 5 episode "Jack of All Trades", Charlie walks back into the FBI office to applause after his security clearance, which was revoked at the end of Season 4, is reinstated.
  • Heterosexual Life-Partners: David and Colby. At least until they decided to play their Ho Yay for laughs.
  • He Who Fights Monsters:
    • In "Dark Matter", the mastermind of the school shooting started off just wanting to get revenge on the classmates who arranged for her to be raped, but somehow ended up deciding to do it in a way that put everyone in the school at risk, even though it was only a small number of students that had anything to do with the incident.
    • This is discussed heavily in "Killer Chat", since it's about a Knight Templar Serial Killer who is murdering child molesters.
      Don: [while interviewing a teenaged suspect] Look, it makes sense you'd want to get back at people like that, with what happened to your sister. It's normal, it's natural; I would, too. But that makes you just like them, right?
      [suspect nods his head "yes"]
      Don: Is that the person you want to be?
      [suspect shakes his head "no"]
  • Hidden Depths: Colby is revealed to speak Spanish, which helped them on a case that had missing Spanish girls.
    • In one episode, Don and Charlie learn that their late mother was a talented musician and composer. The same episode also reveals that Don knows how to play the piano, which then becomes a Chekhov's Skill in a later episode.
    • Another episode has Don revealing that his favorite movie is a 1940s black-and-white comedy.
  • Hilarious Outtakes: A vast majority of the show's outtakes involve Charlie's actor David Krumholtz messing up a line and letting out a stream of curses. Once, however, he stepped right into the Koi pond - which is apparently deeper than it looks.
  • Homage: One episode is one to Scooby-Doo. An abandoned Air Force base is thought by local ConspiracyTheorists to be hosting UFOs or the ghosts of World War II veterans, and when they catch video of balls of energy raining down from the sky and killing a person the FBI gets involved. It starts to look like an Area 51-type Government Conspiracy (the strange Department 44 agent who tags along doesn't help in that regard-though he's surprisingly helpful with the investigation) until it's discovered that the energy was from a Lightning Gun a tech company was working on for the government (the UFO lights people saw were actually from the drone carrying it). The ray was only meant to work like an EMP, and the project's engineers were conducting secret tests to try to make it nonlethal.
    • Lampshaded by Colby when he says, "Why do I feel like I'm in a Scooby-Doo Cartoon?" while they search the base for clues.
    • After the mystery is solved, Charlie muses that the company could have wasted billions more dollars stringing the government along in their refusal to admit the project was a failure. Floyd replies, "Yes, and they would have gotten away with it, too, if it weren't for you meddling kids," referring to Charlie, Amita, and the CalSci plasma physics engineer Charlie asked for help on the case.
  • Hollywood Board Games: Professor Charlie Eppes is scarily Good with Numbers, having attended college at thirteen. This translates to his mastery in playing chess, a game that despite relying primarily on strategy, also requires the same kind of abstract thinking that it's needed to excel at maths. However, when it comes to language, Charlie flunks. This is demonstrated by how he struggles with Scrabble.
  • Hollywood Science:
    • The episode "Backscatter" had, in a background shot, the phrase "Email response IP address: 192.3382.1043.010.255".
    • Another episode involved a coded message whose solution was an IP address with first octet of 275.
  • Honor-Related Abuse: Referenced in an episode involving the murder of an Iraqi woman. The FBI initially speculates that it could be an honor killing, either because the victim had begun speaking publicly about having been raped as a teenager or because she is revealed to have been secretly married a non-Muslim man, but it's ultimately revealed that the actual killer was an associate of her rapist who killed her on the rapist's orders in order to stop her from testifying against him.
  • Hospital Epilogue: The episode "The Fifth Man" ends with the team meeting in Don's hospital room as he is recovering from being stabbed and he and Charlie have a talk about neither wanting Charlie to have Don's life but Charlie promises to see his brother in the FBI office soon.
  • Hostage Video: This is done in "Prime Suspect", in which Ethan Burdick's daughter, Emily, is ransomed for his solution to an equation, with Emily being forced to tell him the demands.
  • Hot Teacher: Amita is young, brilliant, and attractive, and typically wears flattering casual clothes while teaching.
  • How We Got Here: "Blowback" begins with a montage of scenes from late in the episode, then skips back to the beginning of the case.
  • Human Shield: Happens at least twice, both times to Colby. Both times he tells a fellow agent to shoot, but neither does.
  • Hypocrisy Nod: Done by Don when he expresses frustration to his father about his girlfriend, Robin, an AUSA, being skeptical of the story he's telling her, despite having notorious trust issues of his own.
    Don: I don't like not being trusted. And yes, I get the irony.
  • Hypocritical Humor: In the episode "Finders Keepers":
    Millie: Now, I know it sounds like I'm in danger of not having a point here, but I do, and it's this: Out at sea, all bets are off. You encounter forces that you could never, ever anticipate. Granted, some of those forces have to do with, you know, being confined to a very small space with someone who you thought you knew but clearly didn't, someone who is so enamored with the sound of their own voice that they could talk endlessly for hours and hours without ever needing to even have to take a breath...
    Charlie: Millie-
    Millie: (not missing a beat) I mean, you don't know what it's like.
    Charlie: You said you had a point?
  • I Did What I Had to Do: Ian Edgerton from his introduction on, makes the tough calls that Don vacillates over. On one occasion, he is left alone in a room with the blinds closed to extract vital intel from an uncooperative suspect, a decision which has a lasting impact on Don, both morally and professionally.
    • Don gets one himself in "Black Swan", when he tries to justify using what's essentially speculation to hold a man as a domestic terrorist suspect. Charlie questions him after witnessing an unusually frosty exchange between Don and Megan, and Don says this almost verbatim.
    Don: I had to push a rule or two, and, you know, I mean, she disagrees. What else is new?
    Charlie: You had to?
    Don: Yeah, I had to!
    Charlie: Hard not to notice a change in your methods.
    Don: Look, I'm tired of picking up the pieces. Okay? It seems like all we do is get there too late, and I got a chance to stop something before it starts.
  • Idiosyncratic Wipes: The show sometimes does this into (and out of) commercial breaks.
  • Idiot Ball: The FBI has an unlimited supply of those.
    • YMMV on this. Charlie is more of a face for the real life technicians and consultants that would really be used by the FBI. The techniques tend to be rather standard, Charlie is just Mr. Exposition about how the techniques work. And having him as a university professor is fancier than an official FBI analyst.
    • One wonders, how often did the FBI catch criminals before Charlie started helping them? An episode illustrates the FBI's helplessness brilliantly. A man is accused of shooting an FBI negotiator during a face-off with the FBI. He flees after saying he's innocent He really is, and the FBI has been hunting him for months. It's repeatedly mentioned that every cop in the county wants to catch the guy, because he's a suspected cop killer. The bullet that killed the officer flew out of his body, and yet, despite the zeal with which the FBI wants to catch the guy and have him condemned, no one tried to find the bullet that killed their officer, if only to reinforce their case against the guy once they catch him. The bullet is lodged in a tree, with a prominent bullet hole, so it's not like finding it is hard (in fact, once the protagonists decide to look for it, they find it in a few hours) The bullet does prove the guy's innocence, but since no cop knew that, it still wouldn't explain why they never tried to look for it.
      • The idiot ball on that one is played with. The thing is, the house was surrounded by police who were intent on watching the house. They knew there was an armed man inside and they were prepared for that man to fire on them. No one expects a drug company to sell him a tainted vaccine, then when the government catches on to the tainted beef to then hire a sniper to frame the man for murdering a hostage negotiator. Every one at the site, faulty witnesses as they may be, would testify to the fact that they were watching the house at the time of the shot and that the armed man was inside. When they are cops at the scene of the crime negotiating with a man who has threatened to shoot them and then someone gets shot, it's kind of justified to think the same man is shooting. Plus, they had the bullet that was inside the negotiator. They just neglected to make sure that the trajectories were right. Probably because they were storming the building and taking him to cover. Later, they do actually just haul the Idiot Ball around. See the next reference for this episode.
      • In the same episode, it's mentioned how surprising it is to the FBI's expert manhunter that the fugitive never tried to leave his home county, despite it being in his best interest to do so and avoid the intense police presence searching for him. The cops repeatedly found the campsite where he stayed, but just after he's just vacated it. Yet it takes Charlie and his math to reveal the obvious: The man's sticking around his home county because he goes to visit his wife once in a while. Said wife still resides in their home, where the shooting took place. That's right. The FBI, and their expert tracker, NEVER considered that a fugitive who remains near his home might be visiting his family on a regular basis.
    • In another episode, they ask an interviewee if she knows anything about pot. After denying it, she mentions that she doesn't know anything about pot farms. They treat it like a Suspiciously Specific Denial. Of course, they do turn out to be right.
    • Garden variety Idiot Ball that seems to occur just about every episode: agents, usually David & Colby, approach a guy to ask him a few questions, identify themselves from about fifty feet away, guy then looks around nervously and bolts in the opposite direction, leading to a foot chase. These are experienced FBI agents? You'd think they'd have learned by now.
    • A more proper Idiot Ball is with Millie's reaction to the consulting that her professors do. Given the government contracts that could bring in, that seems like something that she should encourage.
  • Idiot Savant: Or "Scan Man" in the case of the titular episode. A savant shows up in the episode working for a parcel delivery service, who can identify a parcel's serial number from just a look at its damaged barcode, but is a compulsive hoarder and barely able to talk with others.
  • I'd Tell You, but Then I'd Have to Kill You: Played straight by Charlie in "Assassin", when Amita is asking him a question about exactly where he learned code phrases (beyond that it was at the NSA) and he replies with the trope. She thinks he's kidding, but he's actually quite serious.
  • If Jesus, Then Aliens: This trope seems to crop up with distressing regularity. Every few episodes, Charlie is challenged to move beyond the empirical world to a matter of faith, only the matter of faith in question is something completely outside the normal debate of science vs. religion, and yet Larry's right there urging Charlie to consider that it might possibly be true. After all, even scientists don't pretend that they can know everything, right?
    • More like Larry's just weird that way. If anything, his entire character exists to pointedly avert the Straw Atheist scientist stereotype while other scientists (like Charlie) take a more traditional view.
  • I Hate Past Me: Played for Laughs when Larry returns from his space mission, then walks into his office that is packed wall-to-wall with his old possessions and documents.
    Larry: This... this is obscene! Who is this person that belongs to this mess?!
  • I Have Your Wife: It happens at least once per season, but fortunately the FBI usually intervenes before anybody can get seriously hurt.
    • "Prime Suspect" involves four criminals kidnapping a mathematician's five-year-old daughter because they believe he solved the Riemann hypothesis, which can be used as a master key for virtually any internet encryption, and they're using her to get the solution as ransom.
    • In "Rampage", the man who shot up the FBI office was coerced by a contract killer hired by an arms dealer to get him acquitted from his current trial to do it or else he'll kill his wife and daughter. Rather than kidnap them outright (which would have tipped off the FBI to the real motive behind the attack), the contract killer uses surveillance photos to show the guy how easy it would be to find them and hurt them. It's also played straighter when a critical witness in that arms dealer's case has his family kidnapped by said contract killer.
    • "Backscatter" has some bank employees captured (one of whom is pregnant) by the Russian mob to coerce their boss into letting them access his bank for their robbery.
    • Crystal Hoyle takes the cake on this one in "Spree"; she kidnaps Megan to extort the FBI to let her partner go. It does turn out there was a little more to it than that; in addition to a hostage, she also swiped the agent's credentials to look up some classified information.
    • In "One Hour", a child is kidnapped to extort a ransom from his multi-millionaire father.
    • "Tabu" appears to be another case of a rich parent's child kidnapped for ransom, but it turns out the "victim" was actually the mastermind.
    • In "Chinese Box", David becomes the hostage of a disgruntled former contractor after trading himself for a woman the man had initially taken hostage.
    • In "End Game", a disgraced former Marine captain wants information from one of his subordinates, so he kidnaps the man's father and sister to force him to give it up. The father is killed for trying to fight back, but the FBI manages to rescue the sister and arrest the hostage takers.
    • In "Jacked", a group of criminals hold an entire busload of tourists hostage to extort a ransom from the bus company. It turns out to be mostly illusion.
    • Toyed with but averted in "Hydra". A child's kidnapping is initially presented to the FBI as a ransom abduction, but the case turns out to be much more complicated.
    • The bad guy in "Shadow Markets" threatens his rival's elderly aunt to force the rival to meet him so he can take his revenge.
  • I Just Shot Marvin in the Face: In one episode, a movie star's friends are being blackmailed, and the secret is this trope.
  • I Just Want to Be Normal: Colby expresses this desire after the reveal that he'd been a triple agent for his entire FBI career. He'd already hinted that he wasn't fond of that assignment, but a scene with him talking to Don makes it clear just far outside the plan this was.
    Colby: What I want is to go back and start over. Have a regular job at the bureau. No lying, no pretending.
    Don: Well, then the question is, can you be happy with a regular job at the bureau?
    Colby: I mean, that's what I set out to do. If I wanted to be a spy, I would have applied somewhere else.
    • He eventually gets his wish. In the following episode, Don decided to keep him on the team. It takes him and David a little longer to work through some of the residual tension, but by the middle of the season, Colby is, for all intents and purposes, a regular field agent, and he remains so through the end of the series (and the series finale implies he doesn't intend to change that).
  • "I Know What We Can Do" Cut: In the episode "Backscatter", two bank employees are taken hostage to force their boss to cooperate with an ATM hacking scheme. The team figures it out and confronts him, and he finally agrees to tell them the truth. His description of what's supposed to happen according to the kidnappers is overlaid over video of him playing his part (basically, appearing to go along with the scheme), intermixed with shots of the FBI's behind-the-scenes actions.
  • Illegal Gambling Den: In one episode, the team uncovered a gambling website where patrons can bet on a Russian Roulette-esque Deadly Game. The premise is that a revolver will be loaded with a single bullet and players take turns pulling the gun's trigger while it's pointed at them. The loser is the one who pulls the trigger while the bullet is in the position where the revolver can actually fire it.
  • I'll Take That as a Compliment: In one episode, Don is being interrogated by an FBI Internal Affairs bureaucrat. A season earlier, the same bureaucrat had dealt with Charlie's violation of security and his fight to get his clearance reinstated. Don gets increasingly irritated and snarky with the bureaucrat, and ends up walking out. As he's leaving, the bureaucrat takes (he thinks) one last shot:
    Bureaucrat: You know, you're a lot like your brother.
    Don: (chuckles as he walks out) I'll take that as a compliment.
  • Imperiled in Pregnancy: One of the bank workers kidnapped in "Backscatter" is pregnant.
  • I'm Standing Right Here: In "Backscatter", Charlie says the trope name word-for-word when he becomes the subject of an argument between Don and Alan.
    Alan: Explain how a mathematician ends up on a case involving the Russian mafia.
    Don: I told him to drop it!
    Alan: You know he can't just drop that stuff!
    Charlie: Hey, I'm standing right here!.
  • Incriminating Indifference: One episode has Liz becoming suspicious when a woman wishes to stay at the FBI officer after being told her husband died. This leads them to realizing he was not actually dead.
  • Incurable Cough of Death: In the episode "Janus List", Taylor Ashby coughed a few times in the beginning before being blown up by one of his bombs. Later, it was revealed that he was poisoned and that he only had a short time to live even if he wasn't burned.
  • Informed Flaw: It's mentioned a couple of times in early seasons that Charlie is a terrible speller, such as when he when he gives an eight-letter word for egotistical as "conceted". It doesn't have much effect on the plot, but it does give his family a means of deflating his ego when they switch games from chess to Scrabble.
  • Infraction Distraction: Used as gambits by some criminals.
    • "Rampage" involves a madman breaking into the FBI office and start shooting the place up, allowing an inside man to smuggle out some confidential data during the evacuation to assist in getting an arms dealer acquitted.
    • "Backscatter" involves Don and his family personally targeted by the Russian Mob, preventing them from looking too closely at the bank the mob is trying to plunder of its secure info.
  • Infrared X-Ray Camera: A variant is used when body-heat signatures pinpointed survivors trapped in the wreckage of a train crash. Arguably might've been justified, in that Charlie sent small camera-armed robots into the wreck to observe the trapped victims directly, rather than through intervening walls. Unfortunately, the signatures of two unlucky victims vanished within seconds of their demise, whereas a real body's heat would take many minutes to disperse.
  • Innocuously Important Episode: The episode "The Mole" is a story about Colby finding out that his old Army buddy is a traitor and having to choose between friendship and honor, and it appears to be pretty well wrapped up by the end of the episode. The events of the episode end up forming the basis for the season finale and subsequent season premiere, where the viewer learns that that case was just the tip of the iceberg. Not only that, Colby has known all along that his friend is a spy, because his friend tried to recruit him too, and Colby's been playing Fake Defector ever since as part of a secret operation to figure out who else is involved.
  • Inspector Javert:
    • FBI Agent Thomas Larson (retired) from Protest is a Deconstruction, convinced that a series of copy-cat antiwar bombings were done by the same suspect from 1960s. Not only was the man innocent, only a suspect because of his political views, and actually died trying to stop more attacks; but Larson himself was the undercover agent who practically gave the actual bomber the blueprints for the original bombings.
    • Lieutenant Walker becomes this in "End of Watch", where after a badge of a missing rookie cop under his command is found, he's certain that the brother of the man the cop killed is responsible. He is furious when he finds out that the rookie cop was killed by one of his own colleagues who turns out to be Dirty.
    • ATF agent Jessica Malloy appears in "Burn Rate", believing that a past suspect of a serial bombing case is up to his old tricks. He isn't, and even has to save her from a bomb himself. In fact, her zealotry in pursuing him the first time caused her to make mistakes that got the whole case thrown out - which is why the copycat bomber chose her as a target and frame the original suspect at the same time.
    • FBI agent Roger Bloom is this to the conman Kevin Oliver, pursuing him for two years. He eventually admits to Don that it became personal when Oliver stole money from a company owned by Bloom's sister, and wanted to catch him both for vengeance and to retire on a high note, even going so far as to steal more cash from the places Oliver hit to get more of the bureau's attention.
  • Inspiration Nod: Season 5 episode 17 contains a number of references to the Robot series of Isaac Asimov, from which it borrows the plot device "an A.I. that kills a human". The episode's title "First Law" after the Asimov's First Law of Robotics. The company in which the death takes place is called "Steel Cave Industries" after one novel in the series, The Caves of Steel. The name of the A.I. accused of murder is "Bailey" after the protagonist of that novel, Det. Lije Bailey. The scientist who is killed is named Daniel and gives his admin password as "Daniel Olivaw" after Lije Bailey's robot sidekick R. Daneel olivaw. Presumably this scientist was the one responsible for naming the A.I. and the company created to fund its development, so his familiarity with these books gives an in-story explanation for all these references.
  • Instant Book Deal: Averted with Charlie, who was offered a book deal by a publisher who saw potential in a mathematics paper he had professionally published on using math principles to make friends (something he found hard to do as a child, made more so as the paper was started when he was nine, and cleaned up to publish). It went through several versions, several titles, and he mentions having to simplify the math so the layman could more easily understand it, until finally becoming a self-help/finding-love book called "The Attraction Equation".
  • Instant Emergency Response: There's several episodes where the team tries to predict specific crimes, based on previously glanced data, and in some of these cases, they actually succeed.
  • Instant Marksman: Just Squeeze Trigger!: Both downplayed and somewhat justified in "Sniper Zero". Charlie's bullet ballistics number-crunching keeps failing to give him the whole picture of how the suspect sniper operates, so he resolves to learn what shooting a gun feels like. After struggling with a rifle at the shooting range for a while, Don gives him a few of the usual pointers: relax his hands, shoot in-between breaths, etc. Charlie's next shot, while not sharpshooter material, is a lot better, and his final prediction on the sniper's nest location is off by only a few feet.
    • Don also points out to Charlie that there's a difference between shooting paper targets and real people. He may primarily be referencing the emotional impact, but the same is true of aiming. (Charlie and David have a similar conversation four seasons later, in which David clearly is referring to marksmanship.)
  • Instantly Proven Wrong: In one episode, David and Colby are trying to arrest an armed terrorism suspect in a garage that the terrorists had been using to build a bomb. David tries to point out to the suspect that he knows better than to fire a gun in a bomb lab, only for the suspect to do exactly that even as David is mid-sentence.
  • Insufferable Genius: Charlie can on occasion be this. Just enough times to give him human faults.
  • Insult Backfire: A mild variation when Don confronts his senior supervisor McGowan in order to reinstate Charlie's security clearance.
    McGowan: You and your brother have the same way of looking at things, you know that?
    Don: (laughs) I haven't heard that but... I'll take it!
  • Interdisciplinary Sleuth: Charlie solves crimes with mathematics!
  • Internal Affairs: In "Power", the FBI works with an internal affairs officer from LAPD to investigate a cop who's been abusing his position to rape women. She's initially reluctant to believe that an LAPD officer could be responisble and is somewhat insensitive to the victims, at one point sending a uniformed officer to transport a victim and completely missing the point when Megan calls her on it. Ultimately, she redeems herself and helps them catch the rapist.
  • Interrupted Intimacy: In "Man Hunt," the FBI tracks down one of the escaped felons to his girlfriend's house, and they raid it to make the arrest just as they're in the middle of having sex.
  • I Owe You My Life: During his time in the military, Colby was rescued by his fellow soldier and close friend Dwayne Carter after their transport was bombed. Carter proceeds to exploit the hell out of Colby's sense of indebtedness after he gets involved with Chinese intelligence, although it's eventually revealed that Colby chose loyalty to his country over his debt to Dwayne and his apparent compliance was an act. Colby finally tells Carter what he really thinks in "Trust Metric".
    Colby: Dwayne, I really wish someone else had pulled me out of that fire.
    Carter: Why?
    Colby: Because I hate owing you.
  • Ironic Echo: A suspect in custody that had stolen a truckload of radioactive material refuses to tell Don where it is and implies that their Dirty Bomb plan is still on, with the smug line "Oh, you didn't think I had a backup plan?" Don later throws that line right back at him when Charlie convinces one of his accomplices to talk instead, right in front of him.
  • I Shall Taunt You: In the episode "Uncertainty Principle", a couple of bank robbers, who just proved to be more competent and dangerous than they first appeared, steal Don's gun in the process of escaping. In the next bank they rob, they show his gun on the security cameras as a way of taunting him.
  • It's All About Me: Chandler in "Hot Shot" has this view of the world, treating others as his playthings. mother seems to have this, albeit a more benign variation, as well, as she appears more concerned with the possibility of Chandler's actions embarrassing her than about the victims he might hurt.
  • It's All My Fault: Don has a habit of falling into the mentality that he's responsible for things that happen around him, even if they're out of his control.
    • In "Trust Metric", he tells Megan that he feels responsible for Colby Granger (who is at that point thought to be a traitor). He doesn't specify his reason, but it's almost certainly to do with how long Colby was under his command.
    • In the series finale, Don loses his gun during an arrest. Even though he couldn't have prevented the loss, he still feels that he would be responsible for any action committed with the lost gun.
  • It's for a Book: Used by the villains of "Dirty Bomb". They contacted a researcher for a nuclear company for information about a particular radioactive isotope (how to handle it safely and stuff like that), claiming they were doing research for a movie script. Because the series takes place in Los Angeles, the researcher wasn't suspicious until she saw an internal Department Of Energy alert warning that three caskets of the isotope was stolen to make a dirty bomb. She subsequently contacted the FBI, which proves useful in finding the identities of the criminals.
  • It's Personal: Happens quite a bit.
    • "Backscatter" has Don try to pull Charlie off the case when the Russian mob they are going after targets him and their father directly. Charlie later realizes they're targeting them on purpose to distract Don from their real target.
    • 'The Janus List"/"Trust Metric" is one of the biggest examples for the team. Megan put it best:
      Megan: Why are we doing this? We're acting like this is any other case, and it isn't.
    • A close runner up is "Two Daughters", which was a normal case until Megan is taken hostage, then it becomes very, very personal. Though Megan herself doesn't seem to feel that way, despite everything that happens.
    • "Breaking Point" has two separate versions of this around the same case. Colby has this from the beginning, identifying with the victim to the point of obsession, while Don starts off professional, but takes it very personally when their antagonist goes after Charlie.
    • Charlie gets the Season Four finale and no less than four separate cases in Season Five (including that season finale as well).
    • A variation occurs with Colby in "Greatest Hits". He clearly sympathizes with Bloom, but he eventually reveals that it's not so much Bloom himself as the fact that Bloom's situation reminds him of what happened to his father (who he suspects killed himself because of it).
  • It's A Small Net After All: In one scene, the investigators set an alarm to trigger whenever someone logs onto IRC as "The_Fist" or "Oozemeister". Apparently, there's only one IRC server in the world, and handles are never shared or changed.
  • Ivy League for Everyone: Mathematical genius Charlie attended Princeton at age 13 for his undergraduate studies. He graduated when he was 16.
    • Larry Fleinhardt also went to Princeton and graduated when he was 19.
    • Robin Brooks went to Harvard Law.
  • I Want Grandkids: Alan takes the proactive approach, giving solid relationship advice to Don and Charlie.
  • I Want You to Meet an Old Friend of Mine:
  • I Will Only Slow You Down: Season 5 pilot "High Exposure" has Don trying to escort a couple of rock climbers away from gunmen, but one of them twists his ankle and, knowing the gunmen want information they think they have, gives himself up to them to allow his friend and Don to escape.

    J-L 
  • Jack Bauer Interrogation Technique:
    • The episode "Two Daughters", in order to find the location of Crystal Hoyle who had kidnapped Megan, Don leaves Ian alone with Buck Winters for several minutes with the blinds drawn. He comes out several minutes later and announces that Buck gave up the location. (It should be noted that this was not used to build a case at all, but it's still the kind of thing that could get them in serious trouble if the higher-ups ever found out about it). It's specifically treated as a case of O.O.C. Is Serious Business; even Don himself comes to regret it later, feeling that he momentarily lost his good sense.
    • Colby later threatens to do this to a subject in "The Fifth Man", and has to be pulled off by David. Particularly noteworthy since Colby was the one who tried to talk Don out of the earlier example. (Admittedly, it's never quite made clear if he actually intended to do what he threatened or if he's just hoping to persuade the suspect with the threat itself).
  • Jack the Ripoff: "Sniper Zero" has a spate of sniper killings with hunting rifles. After the news exposure and the news that the killer is still at large, several other disgruntled individuals use hunting rifles as their M.O. of choice. Once they discover that some cases are independent of the spree, they are solved relatively quickly.
  • Jerk Jock: The Jocks who raped Karen in "Dark Matter" are this.
  • Jerk with a Heart of Gold:
    • The recurring character of LAPD Lt. Gary Walker. He's a gruff and somewhat jaded man, but he cares more than he lets on; if the viewer couldn't tell from his two appearances, it becomes completely clear in "End of Watch", in which Walker must deal with the murder of one of his subordinates.
    • Ian Edgerton too. The man clearly has his own moral code, but at the end of his first episode, he comes running to make sure Charlie is okay. He also covers for Don after the events of "Two Daughters" and is involved in rescuing both Don and Amita when each of them gets into trouble.
    • The entire plot of "Frenemies" is about Marshall Penfield being a Jerk with a heart of gold.
  • Jurisdiction Friction: Zigzagged. Don's FBI crew has a tendency to work and play well with other agencies; they especially have a good relationship with the local cops. However, as shown in "Brutus", the CIA are another story.
    • Zig-zagged in "Finders Keepers". At first the NSA agents are mad at Charlie and the FBI, believing Charlie deliberately sent them on a wild goose chase to help out his brother. However, once it's established that the whole situation really was a monumental coincidence, both sides realize they need to work together and they have no further problems.
  • Just Friends: Charlie and Amita had to remain just friends whilst Amita was still a student (or a student teacher, one or the other) at CalSci. After she became a professor, their relationship blossomed.
  • Just in Time:
    • The pilot episode involving a serial killer has Terry rescue his latest victim before she is suffocated.
    • Season 2 episode "Harvest" has the team searching for an Indian girl before she can have her organs harvested, and they track her and the surgeon down seconds before he starts cutting into her.
    • At the beginning of season 4, Don and his team manage to get to a captured Colby seconds after Lancer sticks the last lethal needle into his chest (but before he pushes the plunger), forcing them to use CPR to revive him.
    • A contract killer has Robin cornered on a pier, but Don, who was tracking Robin through her bugged hairclip, gets there just in time.
  • Justice by Other Legal Means: Mentioned briefly in the series finale. While pursuing a case involving a string of vigilante murders, the FBI questions a man whose daughters' rapist was acquitted, and he tells the FBI that they're planning to sue in civil court, where the burden of proof is lower. As it's only tangential to the plot (the FBI was only concerned with the possibility that he might be looking to kill the rapist), it's not mentioned after that.
  • Just Smile and Nod: The FBI gang do this when Charlie explains some very complicated math theories.
    Charlie: Right, no, we have to consider variegated terrain and a considerable time gap. Compensate for the time lag. Add overlapping search spirals to maximize the area covered...
    Edgerton: ...Anyone else following this?
    Granger: Just nod your head and wait for the punchline.
  • Just Like Robin Hood: One shows up in "Robin Hood", natch, who robs a bank known to have customers with seedy connections and gives the proceeds to charity.
  • Karma Houdini Warranty: In "Dark Matter", Jake Porter (who raped Karen Camden) ALMOST got away with his crimes, since Karen's own crimes mean no one will believe her...but unfortunately for him it turns out one of his friends was stupid enough to take photos of the incident. Upon being informed of this, Porter promptly tries to run, only to get forced to the ground and arrested.
  • Killed Off for Real:
    • Uncertainty Principle: Agent McKnight is killed in a shoot-out while the team is going after seemingly non-violent bank robbers.
    • Trust Metric: Mason Lancer and Dwayne Carter.
  • Killing in Self-Defense: In "Hot Shot", Don is forced to shoot Chandler after Chandler injects him with morphine, as he's about to pass out and can't risk Chandler might do once he's unconscious and unable to defend himself. Charlie and Alan both agree that it was fully justified under the circumstances.
  • Kingmaker Scenario: Brought up in one episode revolving around a rigged voting machine scheme. Since the scheme was done in California, which has the most voting electors, it quickly becomes clear that the masterminds behind the scheme are shaping themselves up to be kingmakers.
  • Knights and Knaves: The FBI catches a pair of criminals who stole a truck full of aid money. One says that the truck is gone while the other says the truck is still there. Charlie believes that the scenario is comparable to this problem, so he tells Don to ask them what the other person is going to say. When the answer from both suspects is the same, that the truck is gone, they know it must still be there.
  • Knight Templar: Several.
    • The man who lost his son to gang violence, and starts setting off "shooting chains" to cause as many gang member casualties as possible.
    • The woman who had her husband molest their daughter, kills him in revenge, and starts tracking down other pedophiles to torture them, get their confessions, and then murder them to prevent other children from being molested.
    • The man who was a victim of a hit-and-run that went cold, who started assaulting every person he sees responsible for road danger.
  • Knight Templar Big Brother: Don... he has gotten better about it over the years, though.
  • Know When to Fold 'Em: The climax of "Prime Suspect" involves a Hostage Situation with the last kidnapper holding a handgun to a girl's head while trying to use her as a Human Shield against the FBI. However, when he notices that Terri has gotten a clear shot at him that would not put his hostage in harm's way, he lets the girl go and surrenders.
  • Ladykiller in Love: Don becomes this when he falls in love with Robin. Though the "ladykiller" part is more of an Informed Attribute than anything.
  • Lady of War: Megan, Liz, and Nikki all fit this trope to varying degrees. Amita has her moments as well.
  • Lap Pillow: Gender-Inverted in some episodes with a few scenes showing Charlie and Amita on the couch together with Amita resting her head on Charlie's lap while he strokes her hair and talks with her.
  • Late-Arrival Spoiler: The show has one for each of the last three seasons, each related to the cliffhanger for the previous season's finale. Mostly related to season memorabilia and DVD/streaming menus.
    • The Season Three finale ends with Colby being exposed as a traitor and arrested. But it's not hard to figure out that Agent Colby Granger will play a role in Season Four, suggesting that he will in some way be exonerated despite having confessed.
      • Spoils a second plot point in "Trust Metric" as well. While Don and the team are trying to figure out whose side Colby is really on, note  Colby is in the hands of his target, who knows exactly where Colby's loyalties lie. The episode itself goes out of its way to preserve the suspense, so it's not until the very end that the viewer even knows if he's going to live or die (the episode actually seems to lean toward the latter). But knowing he appears in later episodes makes it clear that tone way or another, he is going to survive.
      • A third, more more minor plot spoiled at this same time is the question of whether or not Don is going to let Colby back on the team, a question that runs underneath the main plots of several episodes until Don makes the official announcement in the fourth episode of the season.
    • Given Charlie's importance to the show, the very fact that there is a Season Five suggests that the revocation of Charlie's security clearance (which prevents him from consulting with the FBI) will not be a permanent state of affairs. But the fact that several episode descriptions mention Charlie doing something with the FBI doesn't hurt either.
    • The Season Six premiere spends most of the episode (behind the scenes of the actual case) teasing how Amita responded to Charlie's proposal in the Season Five finale. But the descriptions for several Season Six episodes refer to matters having to do with an upcoming wedding ("Charlie and Amita disagree on a wedding date") and the description of the series finale specifically refers to them getting married.
  • Late to the Tragedy: Don has been known to complain that being in law enforcement basically entails this.
    Don: Look, I'm tired of picking up the pieces, okay? It seems like all we do is get there too late.
    • Charlie makes a similar complaint a season later, comparing the FBI to doctors trying to treat car crash victims thrown through windshields (the solution is not to come up with a better way to treat said wounds, but to come up with a means of preventing them, namely seatbelts). He actually tries to figure out a way to prevent crime with math, but is forced to concede that it's too complex a system to be undermined in the way he intended.
  • Latex Perfection: A high-quality rubber mask was worn by a bank robber in an episode and it was totally convincing, though the wearer wasn't impersonating anyone in particular, just concealing his own appearance.
  • Layman's Terms: Once an episode Charlie or one of his colleagues references an obscure mathematical concept that can be used to help solve a case, then creates an analogy to make it understandable. The team has come to expect them and basically ignore the math and wait for the analogy. See Just Smile and Nod.
    • This predictable behavior is lampshaded in "Brutus" when the agent prompts him for the analogy: "Imagine..."
    • Occasionally inverted by Larry for laughs, who takes everyday situations and complicate it by adding cosmological terms.
  • Leave the Two Lovebirds Alone: Charlie and Amita use this trope to give Larry the opportunity to ask Megan out.
    Charlie: Hey, you said we were supposed to do something earlier, remember?
    Amita: What?
    Charlie: Ya'know, you said it let's go.
    Amita: R-right! Bye! (both leave)
    Megan: What was that all about?
    Larry: A very crude attempt at lending privacy.
  • Leet Lingo: The show used leetspeak on occasion. Amita is fluent in leet, often decoding leet passages for Don his FBI team.
  • Letters 2 Numbers: Or, if you prefer, L3tt3rs To Numb3rs. The show also did this in its opening sequence. The names of the actors would slide across the screen to the right as numbers, resolving then into the letters of the actors' names, except for a couple of them, which would remain briefly before then switching over to the letters.
  • Let Off by the Detective: The episode "Robin Hood" involves the robbery of a bank frequented by suspected antiquities smugglers and drug dealers, who are robbed and the proceeds from returning the spoils/retrieving the goods given to charities. When the team finally track down the bandit (who was the brother of a firefighter that died in the arson burning of a homeless services house, orchestrated by the bank manager who wanted to develop the land), they have already arrested the manager for conspiracy of the arson and the arsonist himself, so Don mentions the man's upcoming trip to Venezuela and recommends he stay there for a good long while.
  • Libation for the Dead: In one episode, after the cops Finally Found the Body of a long missing cop and close the book on what had happened to him, Gary Walker ends the episode pouring whiskey onto the gravestone while lamenting about how the killer was right under his nose for all those years and recalling happy memories about the dead cop.
  • Like a Son to Me: When Larry leaves on his sabbatical in Season 6, he leaves a large amount of his work scribbled on a wall with a note that translates to "All to son". Everyone immediately knows he's referring to Charlie.
  • Literal Metaphor: In "Toxin", the agents learn that their suspect is looking for another guy, a fugitive named McHugh, because McHugh's blood contains evidence of a conspiracy the suspect is trying to expose. Megan quips that the suspect "wanted McHugh's blood, literally".
  • Lonely Funeral: In the first season episode, Sacrifice, Charlie went to a funeral of a colleague of Larry's only to see that Larry was the only one there. Larry laments how the man was brilliant and a genius and yet, there was no one else at the funeral except for the two of them.
  • Longer-Than-Life Sentence: "Arrow of Time" reveals that Buck Winters from "Spree" received a 250-year sentence for his crimes in that episode. (And then, he breaks out of prison and kills a man, implying that he'll end up getting even more time tacked onto his sentence.)
  • Lucky Charms Title: The title "Numbers" is stylized as Numb3rs.

    M-O 
  • The Mafiya: In "Backscatter" dealt with a Mafiya boss who threatens Don and his family in order to divert attention from his real plans, leading Don to kick Charlie off the case. It nearly works, except Charlie's brain refuses to stay off, and he eventually figures out the boss's plan, culminating in a rather complicated scheme to nab him. As in many depictions, the boss is portrayed as vicious and brutal. Gary Walker provides the following line.
    You know what they say about the Russian mob? They'll shoot you just to see if the gun is working.
  • Magical Defibrillator: Averted altogether in the season five episode "The Fifth Man". While in the hospital,Don's heart goes into fibrillation and the defibrillator is used to restore a normal rhythm. You can see the monitor displaying an erratic heartbeat. When he flatlines, they use a syringe filled with a drug to attempt to revive him, not the paddles.
  • The Main Characters Do Everything: The show features this with Omnidisciplinary Scientist Charlie, somehow a mathematician is the one they go to handle engineering analysis, geology, and whatever random scientific concepts are necessary for the case of the week. While he does get help from Amita, a computer scientist, and his physicist mentor, Absent-Minded Professor Larry, they are still involved in a much larger number of fields than any real life scientist or mathematician. While occasionally other experts are brought in as necessary, more often than not it falls to three main characters to do all the work.
  • Make It Look Like an Accident: In a late season five episode, Colby Granger mentions that he believes his father, who died when his truck went off a cliff on a mountain road, may have done this to himself. There's no proof either way, but since there's only one small stretch of that road that doesn't have a guardrail between the road and the cliff, Colby finds it a little suspicious that his father just happened to go off the road in that exact spot, especially given that in the days leading up to the incident, he had been depressed over losing his job.
    • A couple of earlier episodes involve situations where a criminal tries to eliminate witnesses without being caught by staging accidents (and in one case a suicide), figuring that no one will connect these apparently separate incidents. In both cases, it works until someone makes a connection between the victims, at which point it becomes clear how unlikely it is to be a coincidence that all of these witnesses would happen to die in accidents within a relatively brief time frame.
  • Mama Bear: A dark example in "Killer Chat"; Elaine Tillman found out that her husband molested their daughter (she knew he was a pedophile, but he had promised her he wouldn't do anything to their children), so she murdered him in revenge. Then she started luring other child molesters to vacant houses under the disguise of a teenaged girl online, torturing them to get their recorded confessions, and then murdering them so no other innocent kid would go through what her daughter went through ever again.
  • Manly Tears: Charlie breaks down in Don's arms when he thinks Amita may have been killed.
  • Married to the Job:
    • This Seems to be the case for a good deal of the cast. David and Colby seem to consider this a badge of honor, or at least an excuse why they aren't in relationships. Nikki meanwhile, while devoted, does try and date. Granted, said relationships don't work out for circumstances (a date bailed because of an unexpected connection and her romance with the sniper was put on hold when he had to serve time.)
  • Martyr Without a Cause: Invoked in one episode by agents questioning a suspect who's part of an extremist anti-government group.
    Suspect: I'm not afraid to be remembered for the cause.
    Don: What cause? Tax evasion?
  • Mathematician's Answer: Although there are few mathematicians in the group, it's actually physicist Larry is the most prone to these.
    Charlie: Larry, is everything all right?
    Larry: Everything? Well, I'm not sure that I can account for the slate of all matter...
  • Maybe Magic, Maybe Mundane:
    • In Hot Shot it's not entirely clear if Alan and Charlie are dreaming or seeing visions of Margaret (JoBeth Williams) but it is treated like they are dreaming.
    • One episode has the Eppes family quarreling about the legitimacy of a psychic, when suddenly a framed photo of Margaret in their house falls down for no apparent reason. Alan comments that their mother hated when her family argued but Charlie points out that it’s not the first time that picture fell since it needs a stronger bracket.
  • Mayincatec: During his time aboard the ISS, Larry makes himself a quipu, a recording device used by Andean South American cultures (e.g. the Inca) consisting of threads of llama or alpaca hair encoded by knots in a base ten system. It was primarily used to record numerical data for tribute payments. Unfortunately, Larry, who appears to know much about them, claims they were used by Aztecs (from North America). Furthermore, he claims to have encoded his memories on them, even though right now it's only being speculated that the quipu were used for more than numerical data and no other meaning has been deciphered.
  • Meaningful Name: Amita Ramanujan. Srinivasa Ramanujan was a very famous mathematician.
  • Meaningless Villain Victory: In the episode "Democracy", the FBI faces a hedge fund investor who rigged an election, and then arranged for all but one of the witnesses to be murdered and has someone else take the fall so he walks free. However, Charlie publishes the math used in the case, so that election officials would know what to look for and stop any other rigged elections.
  • Measuring the Marigolds: Subverted by Charlie in that he appreciates the beauty of the world, he just sees math as playing a part in that beauty.
    • It's later played straight in "Magic Show", where he finds it hard to appreciate a magic performance since he knows there's always a trick behind it. Amita helps him appreciate the trick itself.
  • Meet the In-Laws: In "Pay for Play" Charlie goes to meet Amita's parents and he is nervous about it. Things do get awkward but Amita's parents do eventually accept him when they meet him.
  • Minor Crime Reveals Major Plot:
    • "Calculated Risk" has the FBI investigating the murder of the CFO of a company that just went under, but Charlie's analysis reveals that the murderer killed her because she might've found out that he was embezzling money from the company and then authored a scam to cover it up, which may have also brought the company down behind him.
    • "Black Swan": An apparent innocent bystander at the scene of a drug raid flees from the cops, and the FBI discovers that he's involved in a domestic terrorist bombing plot.
    • An Invoked Trope in "Robin Hood"; a high-tech bank robbery turns out to be the first piece in an intricate scheme to expose the misdeeds of the bank's president, as the bank's president masterminded an arson that led to the death of the robber's brother, a firefighter.
    • "Assassin": While busting a passport forger, the FBI discovers evidence of a plot to murder the last member of an influential South American political family.
    • "Waste Not": A sinkhole suddenly forms underneath an elementary school playground, killing a teacher and injuring several children. During the investigation into why it happened, it's revealed that a construction company has been dumping toxic waste barrels underneath the playgrounds they've built at several low-income schools.
  • Minored In Ass Kicking: Megan Reeves as she may be primarily the psychologist, but she's also a black belt in Krav Maga, and one of the best shots in her entire FBI office. Do not make the mistake of thinking she's soft or won't fight back.
  • Misplaced Retribution:
    • In "Judgement Day", the widow of a murdered cop has this motivation. The detective got killed and his killer caught, but though the jury recommended the death penalty, the judge overruled them and gave him life in prison instead. For years after, the cop killer made numerous appeals for retrials, agonizing the detective's widow with every moment that looked like he'd go free. When she finally couldn't take it anymore, through her husband's old contacts, she found a hitman to go after the judge's wife, to make him think about "the next criminal he goes easy on".
    • The killer in "Traffic" has this on multiple levels. First off, he was injured in a hit-and-run and consequently had no concrete person to blame for his own misfortune, so he displaced that rage by identifying people who had suffered similar injuries and then taking revenge for those incidents. And secondly, he didn't just target people who directly caused accidents, but rather pretty much anyone who was involved other than the injury victims themselves - his targets included accident witnesses and even a tow truck driver.
  • Missing Mom: Don and Charlie's mom died a few years prior to the show. Definitely a case of adult-onset missing mom. Her death is mentioned repeatedly, appropriate given how recently it happened. She makes an appearance in Charlie and Alan's dreams in the Season 2 episode Hotshot.
  • The Missus and the Ex: Don's history causes this to happen a few times.
    • The primary example is Robin Brooks and Liz Warner. Though Liz eventually admits that she always knew that her relationship with Don was really a rebound after Robin broke up with him.
    • An earlier episode has a version of this by proxy, when an officer a case mentions having known Don's (dead) ex-girlfriend, with Liz being the Missus in this situation.
    Don: Hey, what was that look you gave me when Malloy mentioned Nikki Davis?
    Liz: Right, like, "Why is it all your girlfriends are people you've worked with?"
  • Mistaken Age: Charlie was once invited to a bed and breakfast in Santa Monica after publishing his first paper. Unfortunately, he was fourteen at the time and he had to break it off to a very embarrassed female professor in Berkley.
  • Monty Hall Problem: A topic of one of Charlie's lectures in an episode.
  • Mooching Master: Millie accuses Charlie of being this to Amita in one episode. She raises a couple of fair points about how he uses Amita's time, attention, research, and resources for FBI work. This leads to Amita carefully distancing herself... a little.
  • More Dakka: "Arm in Arms" involved a stolen shipment of guns with a frighteningly high firing rate and muzzle velocity - from which Otto calculated that the guns would overheat and explode if they were used for more than short bursts.
  • Motive Misidentification:
    • In "Sacrifice", it initially appears that a researcher was killed to steal his research. In reality, his killer found his research horrifying, and killed him to stop him from completing it.
    • In "Rampage", a man breaks into the FBI office and starts shooting everything up, but only a suspected pedophile the team was interrogating right before the attack is killed. The FBI initially assumes that the attacker was getting revenge on the pedophile for molesting somebody he knew, especially when they find out the attacker has a daughter in the age range that the pedophile liked to prey on. Then it turns out that the pedophile was accidentally hit by a bullet that went through the attacker rather than being shot by the attacker, which destroys the entire theory of motive. It turns out the attack itself was designed to trigger an emergency evacuation so an inside man could smuggle out some confidential data without risking being caught by a security screener on the way out. The attacker himself was an unwilling accomplice, who the contract killer coerced by threatening to kill his family if he didn't do the attack.
    • The Season 2 episode "Backscatter" has Don and his family directly targeted by the Russian Mob after arresting a couple of phishers connected to them near a bank. Don thinks that It's Personal, but in actual fact, they're targeting him to distract him from investigating the bank, which the mob is planning to rob.
    • "Pandora's Box" involves an intentional plane crash, killing five people. The FBI at first thinks it's due to the prototype scramjet being transported on it, when the real purpose was to hide a computer virus on the flight data recorder, get the FAA to hook it up to their mainframe, and insert code that would allow the perpetrator to conceal planes from their radar - perfect for drug smuggling.
    • "Blackout" starts with multiple power substations being vandalized all over the city. Theories are thrown around from causing a cascading failure of the grid to union dissent, before it's revealed that the aim was to drain the fuel supply for a prison's backup generators, so that they'd call in an emergency delivery of fuel. This would allow the bad guys to use the tanker as a Trojan Horse to infiltrate the prison so they can assassinate an inmate who's planning on giving the FBI information about their drug operations in exchange for a lighter sentence.
  • Mr. Fanservice: Charlie and Colby. The former appeals to fans of cuter Pretty Boys and the latter to fans of Hunks. The producers are clearly aware of Charlie's attractiveness, exploit it and often makes him emote and Colby has his own fair share of angst, particularly when it comes to the army. Colby also has a thing for getting into the water, and let's not forget the Ho Yay.
  • Multigenerational Household: Alan and Charlie share the same house. Though part of the show, Charlie is the owner.
  • Multilayer Façade: Colby's allegiance. First he's an FBI agent. Then he's revealed as a Chinese double agent. And, then, no, wait, he's an American spy infiltrating the Chinese. Unsurprisingly, it takes the others a while to figure out what's true and what isn't.
  • murder.com: "Killer Chat"; the case is about a Knight Templar serial killer who targets child molesters and finds victims by posing as a teenage girl online, leads them to an empty house, tortures them to get their recorded confessions, and then finally murder the molesters.
  • Mysterious Past: Other than being in the military as a sniper, which he now does for the FBI, nothing else is known about Ian Edgerton's past.
  • Narrative Profanity Filter:
    • "Counterfeit Reality" has an FBI agent listening in on a suspect's phone call. The suspect is heard saying one "son of a bitch" on the recording before the agent pauses it and summarizes the rest of the call with "So, after 2 minutes and 49 seconds of profanity..."
    • In one episode, when Charlie and Don are recalling how one of their friends (who ultimately grew up to become a professional surfer) had been afraid of water when they were children.
    Don: The high dive. When we were kids, I'd be up there doing back flips off the thing and Nathan would be frozen stiff.
    Charlie: I remember that. I jumped in before he did. He told me that I had courage. (Beat) He used a more colorful term.
  • Nazi Gold: In "Provenance", a Pissaro painting lent to a small art museum is stolen. An old Jewish woman and Holocaust survivor named Erika Hellman, who was born in Berlin, claims that it had belonged to her family before they were all sent to the Nazi death camps, and she has been in a court case with the current owner of the painting (who inherited from his Army veteran father after he bought it when World War Two was over) trying to win ownership of it when the episode starts. Both her grandson, Joel, and the current owner become suspects, the former because he's fiercely protective of his grandmother, and the latter because he had a massive insurance payout on the painting. However, in the end, it's revealed the museum curator stole it because he found out that the painting is a fake, much to everybody else's surprise. The original is found to be sitting in a police vault in Budapest, because Erika's father had commissioned an art forger to recreate the painting and gave him the original for safekeeping so the Nazis would be stealing a fake instead of a priceless painting, and when the Hungarian police arrested the forger in 1946 they had assumed that the painting was one of the fakes they were confiscating as evidence. The episode ends with the Hungarian police sending the real painting to the FBI and Don giving it to Erika and Joel, allowing them to have one piece of their pre-World War II family heritage back.
  • Necro Cam: The show has its own take on this: When Charlie (or in later seasons, Larry or Amita) delivers a Phlebotinum Analogy, often several times an episode, their surroundings fade out and the discussion is overlaid with chalkboard-drawn equations and visual effect sequences representative of the analogy.
  • Needle in a Stack of Needles: The case in "Graphic" involved a very rare comic book being hidden amongst forgeries and all being sold off at an auction.
  • Nerds Are Sexy:
    • Charlie asks Amita on their first date after she solves a particularly tricky mathematical analysis. Later they find out that math is really all they have to talk about, but this doesn't seem to be a problem since they're still together.
    • Megan has a relationship with Larry.
  • Never Going Back to Prison: In "Trust Metric", Dwayne Carter draws his gun on multiple police officers before Colby intervenes and they get away. When Colby asks what he was thinking, he replies, "I was thinking "I'm going to die before I go back to jail'," to which Colby nods grimly. The viewer never does find out what happened to them in prison, but given the nature of the crime as well as the fact that Colby had been a cop, it probably wasn't an easy time for them.
  • Never Suicide:
    • One case is set off by an apparent suicide of an engineering student, which Charlie is convinced was actually a murder because he discovered a big, expensive secret about a skyscraper's faulty construction. While the student did discover the secret flaw, his death was a legitimate suicide because he was already suffering from depression and thought nobody would listen to him any other way. note 
    • Played straight in "Guns and Roses" and "Democracy".
  • Never Win the Lottery: The show had one episode that dealt with people stealing scratchcards in order to decode the relationship between the serial numbers and the distribution system, thereby allowing them to determine where the jackpot-winning ticket would end up so they could buy it. It turns out that the crew were people who had previously won the lottery for real, but had blown through their respective winnings and were looking for a way to recover at least some money to keep their lives from completely falling apart. At the end of the episode, Alan also pranks Charlie with a fake ticket, though he reveals the truth after only a few seconds.
  • New Meat:
    • Colby Granger in season 2 and Nikki Bettancourt in season 5. Colby figures it out pretty quickly (his issue is implied to be more that he's still shaking off the military mindset), but Nikki is in hot water with Don on and off for most of her first season on the show. She does eventually come around, largely because of her guilt over Don's stabbing, and the worst thing she does in Season 6 is throwing herself back into full duty too quickly after a serious car accident.
    • Supposedly, David Sinclair started off as this as well, though in his case, we only know it happened because it's alluded to later. Ironically, his stated issue was the opposite of Nikki and Colby's; he was too cautious and reluctant to take any initiative at all.
  • New Old Flame: Don has a few.
    • In "Counterfeit Reality", Kim Hall, the Secret Service agent working the case, is Don's ex-fiancee from Albuquerque. Since it's still early in the series, it's more of this to Charlie (who didn't even realize Don had been seriously involved with anyone) than to the audience.
    • "Guns and Roses" had Don investigating the murder of an ex-girlfriend he had never mentioned. Somewhat justified in that he apparently had quite a few exes, and there's no reason for him to have mentioned this one in particular until she became the subject of his case.
    • Liz Warner edges into this on her first appearance: She and Don were never actually together, likely in part because he was her teacher, but it's pretty clear by the way they talk about it that there were some mutual feelings even back then.
  • Nice Jewish Boy: Charlie, though non-observant.
  • Non-Action Guy: Charlie and Larry. Though Charlie takes a level in badass later on, he's still on the sidelines for the most part.
  • No Name Given: Don and Charlie's mother's, and Alan's wife, name wasn't revealed for the first two seasons, as she was only mentioned in passing due to her death, though it was eventually revealed to be Margaret Eppes.
  • Noodle Incident:
    • The incident that got Charlie's learner's permit revoked. The only thing we know is that it has something to do with radar guns, which Charlie strenuously insists are unreliable.
    • "Assassin": Charlie's work with the NSA is touched upon as apparently he consulted on something that left him with the knowledge of both the various methods of assassination and how to spot code referring to it. It's not clear if this is the same incident mentioned in "Vector" or a separate one.
  • No Sense of Direction: Larry once called his colleagues from Minneapolis because he couldn't remember whether he was in St. Louis or Cleveland.
  • "Not So Different" Remark: Despite their different paths in life, Don and Charlie are often mentioned to be more alike than they initially appear.
    • In the Pilot, Alan mentions that one of the things they have in common is that they are very thorough.
    • In "Counterfeit Reality", one of Don's ex-girlfriends comments that Charlie's "one part exuberance, two parts obsession" approach to their problem is reminiscent of Don.
    • At the end of "Backscatter", David tells Alan that before he met Don and Charlie, he's never known two brothers who were so different and so very much alike. Alan's response is "Tell me about it." as his sons are squabbling and name-calling each other in the background.
    • In "The Janus List", Don gets an "Eureka!" Moment of the type that the show usually gives to Charlie, and he works through it pretty much the same way Charlie does (only with less math). Charlie even lampshades it.
      Charlie: Is that the face I make when I...?
  • Not Hyperbole: Happens in one episode when Alan wanders in while Charlie and Amita are working on the case of the week.
    Alan: Am I interrupting something?
    Charlie: Just attempting to rescue a busload of tourists being held at gunpoint by four men demanding 18 million dollars. That's all.
    Amita: Unfortunately, he's not joking.
  • Not-So-Harmless Villain: The second episode has a pair of polite bank robbers. They walk in, request the money, say thank you, and walk out. They are even polite enough to hold doors open for people. Really harmless robbers with a cutesy nickname, or so people think until Charlie predicted their target and Don and a team tries to arrest them. That is when they demonstrated that not having needed to call backup is not the same as not having backup, and not having needed to use violence is not the same as being unwilling to use violence. Turns out they are ex-special forces working to a deeper plan and perfectly happy to use assault rifles, car bombs, and expertly knife a janitor that gets in the way- just hadn't needed to before.
  • Obstructive Bureaucrat: Subverted by Floyd Thompson of Department 44. For all of his odd comments about government dealings, if the team directly asks him for certain information, he delivers it.
  • Oh, Crap!:
    • At the end of "Thirteen", a serial killer the team has just arrested is genuinely confused when the FBI talks about him having killed his accomplice, as he had thought the FBI did it. All at once, the agents realize what this means (that a third party not affiliated with either side was the one that did it), but they're unable to react fast enough to prevent the serial killer from meeting the same fate as his accomplice.
    • The episode "Robin Hood" has the FBI and LAPD staking out a motel where a tip said that a drug kingpin was going to make a buy. The cars arrive, the men get out, and then the guns start coming out...
      Lt. Walker: Oh, man. All that hardware; this isn't a buy, this is a hit!
  • Old Man Marrying a Child: The episode "Nine Wives" features a cult that's basically made of this trope - they have a habit of marrying underage girls off to adult men, often multiple girls as once. The leader is stated to have 73 wives, including fourteen-year-old girl he kidnapped and forced to marry him at the beginning of the episode. (The cult also has at least one confirmed case where a man married his own daughter, quite possibly while she was still a minor.)
  • Ominously Open Door: Trope Namer. It happens enough to get a a lampshade hung.
    David: Just once, I wish it was a surprise party behind one of these ominously open doors.
  • Omnidisciplinary Mathematician: While far less egregious than other cases, Charlie is an expert at far more fields of math than is realistic, even for a genius like him.
    • Amita too, occasionally.
  • On the Rebound: Don with Liz after he and Robin break up, implied to be less than a week in between. The speed combined with the fact that he doesn't tell anyone about the breakup causes a lot of the people closest to him to believe it's something else entirely.
    • After Robin and Don have gotten back together, Liz assures her she was just the rebound and Don was always stuck on Robin.
  • The One That Got Away: It is suggested that Robin Brooks is this to Don. thought the trope is later subverted with the couple deciding to give their relationship another shot. They later get engaged.
    • Earlier in the series, a victim's husband suggests that Don was this to the victim.
  • The One Who Made It Out: In "One Hour", Che Lobo, a former gangster turned hip-hop CEO, tells Colby that he wanted his (currently kidnapped) son to be this.
    Che Lobo: I swore I would never let my life touch him. That he'd have a chance to be something better. A few months ago, he tells me he wants a paper route so, so he could be a businessman, just like me. I know that he meant it in all the right ways, because that's the only part of me I ever let him see. When you're nine years old, your dad should be...
    Granger: Superman.
    Lobo: Yeah.
  • Only a Flesh Wound: Ian Edgerton seems to "shoot to wound" in most of the episodes he appears in. He is stated to be the third best sniper in the country, and he does tend to shoot at the hand or forearm rather than the shoulder...
  • The Only One: The FBI agent characters, especially Don, are not exactly incompetent, but it often tends to look like they need Charlie before they can solve cases. Granted, he's one of the main characters, so cases where they didn't need him wouldn't take up whole episodes, but still, there's got to be someone in that office who can catch a criminal without calling a mathematician.
  • One-Shot Character:
    • Walt Merrick, Don's boss who appears in the Pilot to monitor the investigation.
    • Billy Cooper, Don's old partner from his fugitive recovery days.
    • Daniel Shay, a young boy Don takes care of during "Calculated Risk" after his mother is killed.
  • One-Word Title: Every season has a few episodes titled this way.
    • Season One: Pilot, Vector, Sabotage, Sacrifice.
    • Season Two: Obsession, Assassin, Convergence, Toxin, Scorched, Harvest, Protest, Rampage, Undercurrents.
    • Season Three:, Spree, Provenance, Traffic, Longshot, Blackout, Hardball, Brutus, Contenders, Democracy.
    • Season Four: Velocity, Thirteen, Primacy, Tabu, Graphic, Power, Checkmate.
    • Season Five: Blowback, Frenemies, Jacked, Sneakerhead, Disturbed.
    • Season Six: Hangman, Hydra, Dreamland, Ultimatum, Scratch.
  • On Three: Delivered by David to Colby, via a Multitasked Conversation, when a gunman has them dead to rights.
    David: Give us one good reason why you're doing this. Okay? Give us two reasons. (Beat) Three!
    (David and Colby spin around and start firing.)
  • Only Bad Guys Call Their Lawyers: Played With. While some of the bad guys do have lawyers, innocent people do occasionally bring a lawyer along when they're being interviewed by the agents.
    • For an example of an aversion, in "Harvest", a kidney failure patient who needed a transplant was discovered with an illegal kidney that he got from a Back-Alley Doctor. The patient's actual doctor immediately contacted his hospital's legal department since he knew law enforcement was going to notice the black-market organ. At the time, the doctor didn't know a girl was accidentally killed in order to get the kidney, but he knew that the incident was going to be investigated and that he would be questioned as part of it, so the legal department paired him up with a lawyer for when Megan went to interview him and collect his patient's medical information as evidence. His having sought legal counsel is never treated as a sign of guilt.
    • It's played straight in "Waste Not"; not only was the lawyer employed by a shady construction company he was a willing accomplice in the crimes the construction company comitted.
    • Another aversion shows up in "Dark Matter". Two teenagers go on a shooting rampage at their high school and when the FBI finds out there was a third shooter, all the members of the school's video game club become suspects because the two shooters were avid members of the club and were the closest to them out of anybody at the school. Their parents respond by hiring lawyers to help defend their innocence. While the FBI agents react with slight annoyance at this because it impedes their investigation, it's never treated as a cause for increased suspicion. At the end it turns out that the third shooter wasn't involved with the video game club at all; she was a school newspaper club friend of the other two shooters who was raped at a party and masterminded the school shooting to get revenge on the people involved.
  • Open Mouth, Insert Foot: When Don first goes to the department shrink, he is originally dismissive and criticizes the shrink for working out of a textbook with no idea what the FBI is like. He changes his tune when the shrink reveals his own past in undercover narcotics, and doesn't appreciate Don not respecting his past job and expecting him to respect his.
  • Oral Fixation: Don is usually seen chewing gum when he is keyed up during climatic scenes, mostly waiting for the suspect.
  • Organ Theft: In "Harvest", four Indian girls come to the United States, each intending to sell a kidney willingly on the black market to get money for their poverty-stricken families. However, the first girl accidentally dies from a surgical error, and one of the other girls ran and hid inside another part of the hotel basement during the chaos caused by the mistake and was taken into FBI protective custody as a crucial witness when Don and David investigated the disturbance in the hotel and found her. The Back-Alley Doctor running the organ ring subsequently decides to kill the two girls he has left in order to harvest all their organs for the money and to get rid of any potential witnesses. One of the girls ends up dead, but fortunately, the FBI interrupts just before the procedure on the second girl begins (coincidentally, the girl in question was the sister of the girl who was in FBI protective custody), and she is rescued unharmed.
  • Organization with Unlimited Funding: DARPA is mentioned several times as this, specifically using the words "unlimited funding". They end up throwing it at 5-year projects. One character, who tries to scam them with a fake AI, claims no one would suspect a thing, as 95% of DARPA-funded projects are failures. And then it turns out that the US government also has a detachment of people who are literally The Men in Black to go after people who are scamming them for research funds.
  • Orgy of Evidence: The show had one episode where Don's team worked with the ATF to investigate a series of copycat bombings, zeroing on a disgruntled scientist who was suspected of the originals (he wasn't but did write the manifesto that inspired the culprit). It was actually a Frame-Up as revenge and it almost worked. The one thing the bomber didn't count on was Charlie, who viewed the case from a purely analytical point of view and found the data "too good". There were no outliers or false data ("a perfect storm of data points that fit together perfectly") which isn't at all possible, convincing the team to look again and they discover the truth.
  • Outlaw Couple: Crystal Hoyle and Buck Winters. Crystal is the one in charge; she is almost twice Buck's age and his former teacher.

    P-R 
  • Pædo Hunt: "Killer Chat" involves a Serial Killer that lures in, tortures, and murders child molesters.
  • Papa Wolf: Do not try to hurt any of Don's team. And DO NOT try to hurt Charlie.
  • Paralysis by Analysis: Alan doesn't understand why the CalSci Basketball team is so poor (although Charlie points out, not unreasonably, that it's not really a burning concern for a bunch of science geeks) and convinces Charlie to try to improve them using "Scientific Methods". This only results in increasing frustration for Charlie as his methods fail to achieve anything. Ultimately, they only win thanks to Alan bringing in a couple of Ringers.
  • Paranormal Episode: The show has a couple examples with Simon Kraft, a supposed psychic and former CIA spook who assisted the team while butting heads with everyone because how he is Creepy Good. His initial appearance had him butt heads with the skeptical Charlie and to test his skill, undergo a card test to guess the suit of cards of a playing deck. Simon gets every single one of the fifty two cards wrong... which Charlie quickly realizes that it's the same probability of getting them all right. He initially leaves the case in frustration, but Simon's lingering words have him come back since the case is more important than their debacle. His predictions are all correct.
    • Kraft returns in the Chinatown centric episode, where he finds the Eppes family home and predicts a murder with his drawings. he teams up with the FBI after being let go. His drawings remain accurate in finding bodies and he also discovers another corpse. However, he ultimately dies when filming a kidnapping (due to trying to pitch a show idea called "Simon Says") and getting run over by the vehicle belonging to the criminal.
  • Parental Abandonment: Not quite, but Amita's parents are always too busy to see her.
  • Parental Incest:
    • In "Nine Wives", which centers around an Expy of the FLDS, a girl finds out that she is the product of this — her father married his own daughter, who was apparently so brainwashed that this didn't register as wrong or problematic to her. The girl, who has largely broken out of the cult brainwashing, was not happy about this.
    • "In Plain Sight" features a child pornographer who's been molesting his own daughter; when the mother found out and tried to get the kid away from him, he claimed she was the abusive one and that she had kidnapped the child in an attempt to keep abusing her. Fortunately for everyone except him, the perpetrator was also a Cop Killer, so the FBI had dug into his background and already found evidence of his abuse.
    • The Knight Templar Serial Killer in "Killer Chat" started tracking down and murdering child molesters because she found out that her husband molested their daughter. In fact, he was her first victim.
  • Parental Marriage Veto: Subverted. Amita and Charlie are both very worried that Amita's parents won't approve of Charlie because he's not Indian, but when they finally actually meet Charlie, they are immediately won over.
  • Parental Substitute: Alan has a habit of acting like this towards Don's FBI team, as well as Robin and Amita (his eventual daughters-in-law). He also takes something of a big brother/mentor role to Larry, providing him with guidance and advice.
  • Pay Evil unto Evil: The Theme Serial Killer of "Thirteen" is sniped while in FBI custody by a soldier who was the boyfriend of his very first victim.
  • Perma-Stubble: Charlie has varying amounts of stubble throughout the show,
  • Perp Sweating: Happens a lot.
  • Person as Verb: Person as adjective. Apparently, sometimes the only way to describe Larry is as himself.
    Charlie: Hey, hey, don't get all Fleinhardt on me.
    Larry: Fleinhardt? Since when did my last name become a predicate adjective?
    Charlie: Since your students started using it that way.
    • A fully straight example occurs in a later episode, when Charlie tells Larry, who is employing a Mathematician's Answer, to "Stop trying to Fleinhardt your way around answering me."
  • Perspective Reversal: Played for Laughs in one episode. Larry and Alan both agree to resolve a disagreement by conceding to each other's points...which leads to a whole new argument as each of them argues the merits of the other's position.
  • The Philosopher: Larry, who stayed at a Buddhist monastery for quite a long time and often nudges Charlie in matters of philosophy. Somewhat of a Justified Trope—he studies quantum physics.
  • Phlebotinum Analogy: Charlie often uses these so he can explain his mathematical analyses to those around him.
    Megan: I'm so hoping you have one of those cute little analogies for this.
    Charlie: As a matter of fact, I do.
  • Picky Eater: Larry spends a couple years eating only white food as an experiment.
  • Pilot: The show had two pilots, the original unaired pilot had Gabriel Macht as Don, Len Cariou as Alan and Jennifer Bransford as Terry while the second aired pilot has Rob Morrow, Judd Hirsch, and Sabrina Lloyd replacing them. Only David Krumholtz, Peter MacNicol, Navi Rawat, and Alimi Ballard appear in both pilots.
  • Platonic Declaration of Love: In the episode "Contenders", which serves as a Heartwarming moment for David Sinclair and his childhood friend Ben Ellis, who had been at odds for several decades following the death of another friend (David blamed Ben for getting their friend killed, and Ben resented David for abandoning him and never giving him a chance to tell his side of the story). At the end of the episode, after they've sorted out their problems, David hugs Ben and tells him, "Love you, brother".
  • Plausible Deniability: Lampshaded and Played for Laughs in one episode, when Liz walks in on a planning session for an almost certainly illegal CalSci prank.
  • Playing the Victim Card: The main villain of "The Running Man", while faking it the whole time. He claims that his mediocre origins kept him from getting into prestigious colleges in favor of the applicants with hard-luck stories, so he re-enters universities under different names and personas and always with hard-luck origins to sympathize his way in and to get the false celebrity of being a person who beat impossible odds for a better life, vanishing after a year and stealing expensive equipment to finance his schemes. David isn't particularly convinced when the suspect keeps bragging about his rough origins (since he knows from experience that hard beginnings are also things one might want to distance oneself from) and isn't particularly sympathetic when they finally catch him.
  • Please Shoot the Messenger: The episode "Checkmate" revolves around a gang leader in prison who gets hit targets to his gang encoded in chess lessons to a young kid. Then a lesson comes in which, once decoded, tells the gang to kill that kid.
  • Poor Communication Kills: Present in David's bad neighborhood backstory: he was so convinced that his Hot-Blooded friend Ben Ellis was the one that started a fight that got Earl Day, the third member of their trio, shot that he never visited Ben in prison, which means he never learned that the normally calm Earl had confronted a guy who was messing with his girlfriend, and the guy responded by shooting him, but Ben took a plea bargain because he knew no one would believe him. David only learns it when his and Ben's paths cross in "Contender", and they eventually make peace.
  • Poster-Gallery Bedroom: A minor plot point in "The Running Man". The team is investigating the disappearance of Ron Allen, so they go to check out his dorm room. They quickly realize that the posters in his room are a bit too calculated, leading them to suspect that he had a double life.
  • Posthumous Character: Margaret Eppes, who died of cancer sometime before the series began.
  • Pregnant Hostage: "Backscatter".
  • Prescience by Analysis: Charlie uses math to predict crimes before they can happen.
  • Previously on…: The show loves this trope. Especially notable since their two-part episodes very rarely end on obvious cliffhangers; the recap is often the first indication that the earlier episode's plot is going to come back in some way (though the level of significance of the previous episode varies).
    • The show show would also have non-consecutive sequels, with the most obvious being "Arrow of Time" (a Season 5 sequel to the Season 3 episode, "2 Daughters").
    • Subverted in "The Janus List", which is a fairly direct sequel to "The Mole" but doesn't use the recap, likely because the connection is not immediately obvious and alerting viewers to it would spoil The Reveal. (Clips from both "The Mole" and "The Janus List" were used in the recap in "Trust Metric", the final episode in the arc.)
  • Prisoner's Dilemma: Utilized in the Season 1 episode "Dirty Bomb". With three perps in custody and none of them willing to talk, Charlie first explains the dilemma to Don and then implements a variation: put all three perps in the same room and have Charlie numerically spell out for them which of them has (or doesn't have) the most to lose by going to prison and the most to gain by talking. Despite exhortations from the ringleader (who has the least to lose), the one with the most to lose eventually decides to talk.
  • The Professor: Larry and Charlie. Especially Charlie, who is incredibly smart and was once a Teen Genius.
  • The Profiler: Megan's specialty.
  • Promotion to Opening Titles: Dylan Bruno (Colby Granger) in season 3 after being recurring in season 2.
  • Properly Paranoid: "Chinese Box" features FBI-contracted surveillance professional who is convinced an agent he used to work for is spying on him. They eventually determine that he's right and, what's more, he had evidence. (He had had some fears about being about being spied on even before this, but it's pretty clear that this incident is what escalated it from a mild concern to a major case of paranoia.)
    Liz: Just because you're paranoid doesn't mean that everyone isn't watching.
  • Public Secret Message: In "Counterfeit Reality", an artist is kidnapped by a gang of forgers to replicate the art on dollar bills for them, but secretly puts imperfections in the counterfeit bills that, when viewed a certain way, provides the FBI with her location, just like how she encodes messages to her husband in her art.
  • Put Down Your Gun and Step Away: In the episode "Jacked", the team refuses to do so during the final standoff, by which point they've realized the hijackers are bluffing. The hostages are afraid to leave after seeing another hostage killed, but it was actually all staged. Once the remaining hostages see the "dead" hostage alive and well, they stop listening to the hijackers.
  • Put on a Bus: When Peter MacNicol did a stint on 24, Larry was Put On A Space Station.
  • Quirky Curls: Charlie is a male example.
  • Rail Enthusiast: One episode that had recreated crashes featured a couple of these guys as witnesses. Their footage of the train provides a vital clue to cracking the case.
  • Rape Is a Special Kind of Evil: The darkest episodes of the series are ones that resolve around Serial Killers and rape. It tells you something when in the episode "Dark Matter" the perpetrator who orchestrated a school-shooting is portrayed somewhat sympathetically: all the students deliberately targeted, including her best friend, were complicit in a plot to have her raped after doing a school article on steroid abuse by the school teams. The sole surviving conspiracist is treated as a Jerkass about to get a taste of his own medicine.
  • "Rashomon"-Style: Inverted in "Hollywood Homicide". While reviewing the witness accounts of the crime that led to the death of an actor's brother, they realize that the statements are too similar: they're almost word-for-word identical, when some level of difference (even if it's just, like, one person recalling a detail that the others didn't notice) would be normal and expected. This leads the agents to believe that the witnesses may have been telling a fabricated story rather than the truth.
  • Real Time: The third season episode "One Hour", in which, while Don talks with his therapist (who has made him turn off his cell phone), the rest of the team has just one hour to crack a case.
  • Reasonable Authority Figure: Don is a textbook example. He's not afraid to give his team members a talking-to when he feels they deserve it, but he by and large treats them as equals and listens to what they have to say, and he even lets Colby back on the team after finding out he was a triple agent. In fact, if he starts shutting his team down or refusing to listen, it's a pretty clear sign that he's in a bad place mentally.
    • The series also shows Charlie to be this as a teacher.
  • Redemption Equals Death: Dwayne Carter, when he shoots Mason Lancer just before he injects Colby with a lethal chemical and gets shot himself shortly after, or at least as close as he ever gets to redemption.
  • Red Shirt: Averted. In one episode, a squad infiltrates a hidden marijuana farm, with several no-named agents. After having specifically stated that those kinds of farms are booby-trapped, it results in an anticlimax where several are disarmed, and nobody gets hurt.
  • Religion of Evil: One episode features a cult based around the idea that "the way to heaven is by marrying virgins - as many as possible". In practice, this takes the form of marrying underage girls off to adult men, often several girls at once to the same man. The cult leader also has been known to kill his own followers if they defy him (and sometimes, like in the episode's climax, just because it's expedient).
  • Remember the New Guy?: Colby and Megan are introduced in Season 2 with little fanfare or even proper character introductions. They're simply dropped into the team like it's no big deal. Justified, as the FBI is a large bureaucratic organization and these sorts of personnel changes are probably so commonplace as to really not be that big a deal.
  • Remember When You Blew Up a Sun?: Colby Granger from Season 4-6 gets several comments referring to the fact that he was a triple agent.
  • Revealing Cover Up:
    • This was the plot of the bad guys in the second season episode "Rampage". A man (who was a perfectly innocent civilian dad aside from having a brown belt in martial arts) was blackmailed into going on a shooting rampage in the FBI building and provoke an emergency evacuation in order to cover up getting a list of key witnesses in a trial out of the building. In a slight subversion, while the FBI was able to connect the shooter to the criminal, the guy was off the grid (he was a hired gun not directly affiliated with anyone) so the trail seemed to stop with him. The break came when Charlie analyzed the shooter's path, discovering that the only conscious choice he made was to avoid shooting anywhere near two guys under a desk. When one of them tried to run, the FBI figured out he was the one who had a connection to the shooter and searched his computer records, which revealed what he'd been doing.
    • The villain of "End of Watch" ends up doing this when the FBI gets on the case of a murdered rookie cop; he kills one of the few witnesses who could tie the whole scheme together by making him OD on drugs - a specific formula of drugs in police lockup that he as the head of the narcotics police raid team that made the bust had access to.
    • "Democracy" has a billionaire murdering anyone who knows of his plan to fix California's election system in ways to Make It Look Like an Accident, but Charlie, given a list of victims, eventually figures out the connection.
  • Rewatch Bonus: The episode "The Mole" seems, the first time around, like a simple story of Colby getting caught between his friend and his job, but takes on a whole new layer of meaning when the viewer knows what's really going on behind the scenes with Colby and Dwayne (as revealed in the "Janus List"/"Trust Metric" two-parter).
  • Rewind, Replay, Repeat: Don begins the episode "Trust Metric" watching Colby's confession over and over, because something about it doesn't feel right to him but he can't quite figure out what.
    • In a later episode, he does something similar, watching a suspect's prison psych interviews repeatedly in an attempt to find an angle. It ends up paying off hugely, as he uses the information he gleans to manipulate one of the supsect's disciples into giving up the location of their hideout.
  • Rich Kid Turned Social Activist: Zig-zagged in the episode "Tabu". An heiress joined up with an underground anti-capitalist organization, but Megan deduces that she's just using the group to lash out at her billionaire father and doesn't really care about the underlying cause.
  • Right Behind Me: One episode has Colby quipping that they should get the "whiz-kid" in to take a look at a case, right as Charlie enters the scene. Charlie chooses to take it as a compliment.
  • Right for the Wrong Reasons: In "Rampage", the FBI initially assumes that the guy who attacked the FBI office did so to protect his young daughter from a suspected pedophile the team was interrogating at the time, since he was the only fatality. It turns out that the attacker's actions were motivated by a desire to protect his daughter... because a contract killer who needed a distraction for an inside man to smuggle out top-secret information threatened to kill her, along with her mother, if the man refused to do the shooting rampage.
  • Ripped from the Headlines:
    • "Sniper Zero" (S01, E09) seemed to be all about the Beltway Sniper Attacks.
    • In "Calculated Risk" (S02, E04), it sounded like they were reading directly from Enron's wikipedia page.
  • Rock–Paper–Scissors: After two other RPS, Charlie begins to explain some mathematical strategies to FBI agents. He stops short and says he'll save them in case he "has to throw down with them" someday.
  • Romanticism Versus Enlightenment: The show might be a poster boy show for Enlightenment but Larry is a romantic and often has friendly tension with Charlie about this.
  • Room Full of Crazy: Charlie is prone to Room Full of Crazy break outs of Math equations at the best of times, but in the episode "Uncertainty Principle", he goes off the deep end when he went into a fit of depression and attempts to solve an apparently unsolvable math problem.note 
    • There's his serial-killer theory in the fifth season, where he fills his office with papers hanging from strings to try and track one killer he believes to be behind over thirty murders. They even bring in a conspiracy nut to help! He's right, of course.
  • Rule of Pool: If there is a pool (or any water, really) Colby will end up in it.
  • The Runaway: In "Money for Nothing", Don tells his therapist that Charlie disappeared during a camping trip with Don's friends and was missing about half a day. Charlie then tells Don what really happened; he knew Don didn't want him there, so he decided to leave and try to walk home.
  • Running Gag:
    • Alan walking in on Charlie and Larry doing some experiments in their house, from building a model complex out of cereal boxes, measuring how ice melts with the house's thermostat, or messing with the shower.
    • A popular one in the later seasons is that whenever the FBI field agents go to a potential suspect, and the suspects run, the agents tend to treat it more as an annoyance than an actual worry that the suspect might get away.
    • There's also one that surfaces occasionally in Charlie's tendency to mistreat whatever random food happens to be lying around to demonstrate a math concept.
  • Russian Roulette: Used as a way to make money from very desperate gamblers and really sick viewers. The organizers even gave the players nicknames and everything; unfortunately for them, it was rigged.
  • Ruthless Foreign Gangsters: In the episode "Backscatter", the Eppes family is targeted by the Russian Mob.

    S-U 
  • Screw the Rules, I'm Doing What's Right!:
    • The finale of season 4: one of Charlie's coworkers is arrested by the FBI because he was sending his biotech research overseas to Pakistan, which the bureau is concerned about even though the research is focused on crop development and is unlikely to be weaponized. At the end of the episode, Charlie sends the rest of his colleague's crop research to Pakistan, then turns himself in to federal custody, and although the charges are dropped, Charlie's security clearance is revoked.
    • In an early season 5 episode, Don brings Charlie in on a case even though his clearance was recently revoked, due to the intensity of the perpetrators.
  • Secret Relationship: It turns out in the season two episode "All's Fair" that the suspect, Lt. Joe Karnes, and the victim, Saida, a Muslim, were married and he tries to avenge her death before the team locates him.
  • Self-Fulfilling Prophecy:
    • In "Assassin", the titular assassin is sent after Gabriel Ruiz by the corrupt Colombian government because his family still carries weight in the movement for reform. Gabriel is introduced outright saying he has no intention of ever returning only to change his mind in the aftermath to honor his father and brother's sacrifice by finishing what they started.
    • In "Trouble in Chinatown" , Simon Kraft predicts the killers' next move and goes there with his camera. The killers are there, along with their big truck. He doesn't get better, either.
  • Serial Killer: The series has had quite a few, from serial snipers to people staging fake car accidents to a murderer killing people in ways that mirror the death of every one of Jesus' apostles. Most of them only appear in one episode. This being a show about Math fighting crimes, all the serial killers are found using math.
  • Serial Spouse: Gary Walker mentions in "Robin Hood" that he has been married and divorced three times.
  • Sexy Discretion Shot:
    • Implied at the end of "Checkmate". Don and Robin are leaving a hotel after Robin was put under witness protection, and reigniting their Old Flame after their previous breakup. Don comments that the room is still paid for by the FBI and they never did have their candlelit dinner, then he grabs the room keys back off the front desk and the two hurry back upstairs. The grin that the receptionists share say it all.
  • Shameful Strip: Liz has to do this in an undercover assignment, to spot bugs. Blatant Fanservice, what with the promos advertising the strip and the random lingerie she just happened to be wearing. The shame bit's still there, though.
  • Sharpshooter Fallacy: The fallacy is mentioned in-universe in one episode by Charlie after Megan mentions that a school recently had a playground cave-in also seems to have an unusually high rate of cancer among students; he suggests that the cancer rate only seems significant because they're actively looking for something out of the ordinary. It's subverted a few moments later when they find evidence suggesting there actually is a connection between the two (which ultimately turns out to be the case).
  • Shipper on Deck: Nikki seems to be this with David and Colby. She's made several comments about the two of them in a relationship.
    • Alan tends to be this for any potential serious relationship involving his sons, and the brothers are this at times for each other as well.
    • Alan and Charlie for Larry and Megan.
  • Shorter Means Smarter: Charlie.
  • Shout-Out:
    • In "Hardball", Colby references Blade Runner, saying that he thinks Ridley Scott knew what the future was going to look like; Ridley Scott is one of the show's producers.
    • The Slobbering David Krumholtz Groupies, a fanclub devoted to star David Krumholtz, received a shoutout in one episode when a company called "SDKG electronics" was mentioned.
    • Bill Nye sometimes appears to give a science demonstration - just like the ones he used to do on his children's educational program - to help the team solve the case.
    • Agent Floyd does the CSI: Miami Quip to Black (minus the "to black")/Glasses Pull gag a couple of times.
  • Sibling Team: Don and Charlie.
  • Sibling Yin-Yang: Don is more "jock-like" and Charlie is more "geek-like".
  • Single Serving Friend: Billy Cooper, who Don worked with in Fugitive Recovery before the start of the series, only appears in the first season finale, "Manhunt".
  • The Singularity: Amita mentions it in the episode "First Law", when a true artificial intelligence may have been created. She seems very sad when it turns out to be a fake, brute-force expert system.
  • Sitcom Arch-Nemesis: Marshall Pennfield, who is Charlie's old rival from Princeton. Near the start of the season two episode: "Convergence", he performs a lecture in which he finds a flaw in the Eppes Convergence, the mathematical theorem that made Charlie famous. Charlie will readily admit that Pennfield is brilliant; he just doesn't like him because he's an insufferable asshole. In the end, Pennfield helps Charlie figure out the case of the week, and when Charlie does find a way around Pennfield's problem, he calls it the Pennfield variation.
  • Skepticism Failure: Seen in "Mind Games" where Charlie scoffs at a psychic who's brought in to work on a case; Charlie is treated as the unreasonable one, surprisingly for a show that focuses on math and logic to solve crimes. He returns in a later episode, but by the end of the episode he's dead and everyone wonders if he was the real deal.
  • Slow Electricity: In one episode, the case involves several electrical out-stations being taken down in an attempt to create a cascading failure. The shot of the shutdown when it occurs is basically the same thing as most shows/movies though, but it's a bit more valid than a full electrical failure causing the skyline shutdown sequence.
  • Small Role, Big Impact: Ronald Haldane as he is only in the pilot episode, and has two or three lines of dialogue, but his crimes are what inspire Don and Charlie to begin teaming up on cases.
  • Smart People Play Chess: It isn't enough that Charlie Eppes could multiply four-digit numbers in his head when he was three, graduated from high school and entered Princeton at 13, completed his bachelors degree in three years and is a multiple PhD. No, just so we'll know he's really smart, he regularly beats his father and his former academic adviser (both portrayed as above-average intelligence) at chess, too.
    • Justified. Chess is a proponent of game theory with a zero-sum outcome in which all information is available and possible moves are restricted based on previous moves. Hence it really comes down to a calculation of possible outcomes weighed against a target outcome. The reason why mathematicians tend to be good at chess is because chess is based in a very specific form of game theory. Why does Charlie always play and always win? Because he's Good with Numbers, chess is about as close as game theory gets to pure mathematics, and he's a mathematician. Although, considering that most of his math deals with statistical models and application it would probably be more appropriate for him to be playing black jack.
      • Which Dr Fleinhart did to the point of being banned from casinos, making him doubly smart!
    • It's been shown that the only way to have a reasonable chance at beating Charlie at chess is for two people to play against him at once while also having a distraction.
    • Mostly averted with Millie, who, after challenging Alan to a game, admits to Charlie that she's never actually learned how to play and has to try and learn the game in the day and a half before she's set to play him. She does beat him, but her approach to the game is less pure strategy and more about people-reading, almost like a game of poker — since Alan is legitimately good at chess, she just reads his reactions to gauge what her next move should be.
  • Smurfette Principle: At least early on in the series. The cast is mostly male with one female FBI agent at a time (Terry first, then Megan takes her place) and Amita. This is then subverted in Season 3 when they add Liz, but Amita is still the only female character who lasted the whole series.
    • That's more a case of Real Life Writes the Plot, as the actresses who played Terry and Megan both left the show for personal reasons.
  • The Snack Is More Interesting: When the FBI goes to arrest the Smug Snake boss in "Longshot", he ignores the agents in favor of his nice sea bass lunch. A very unamused Don flips his lunch plate over to kill his attitude.
  • Soft Glass: Subverted in one episode. One perp attempted to escape pursuing FBI by crashing out of his bedroom window, but not being a particularly strong man, the window steadfastly remained unbroken.
  • Sole Survivor: In "Provenance", Erika Hellman was the only member of her family in Berlin who survived the Holocaust, and was six years old at the time.
    Erika: You have no idea what it's like to be the only survivor of your family and to have no idea why.
  • Somebody Set Up Us the Bomb: The episode "Cover Me" has a flashbang grenade delivered in a duffel bag.
  • Soundtrack Dissonance: The most Egregious example: at the beginning of one episode, the song "Drift Away" plays in the background as a woman is driving home...and continues playing as she pulls into the garage and is killed by an unseen gunman.
    • The end of one episode which has the team doing the required chase sequence, while sad music plays. Then again, there WAS also someone about to be executed for a crime he didn't really commit, so it was fairly fitting.
    • Invoked in the Season 4 episode "Thirteen" which has the killer using Bible Numerology to choose his victims, then recording and killing them in ways that Jesus' apostles were killed (even their names are the same) all while playing soothing music in the background.
  • Space Episode: Larry goes to the ISS for several months.
  • Spanner in the Works:
    • The killer acts as a villainous version of this for Charlie in the pilot episode: He develops an equation that is meant to identify the killer's home based on the locations of his previous offenses and it would have done exactly that if not for the fact that the killer happened to move out of the identified area a few weeks earlier.
    • In "Bettor or Worse", the plan for a jewelry store manager with massive gambling debts and a bookie in a lot of trouble to pay off their associates by arranging for the manager's family to be kidnapped and for the bookie's sister to rob the store is derailed by the lone security guard shooting the robber.
  • Speak Friend and Enter: Sometimes solutions to problems or codes turn out to be easier than Charlie expects.
    • In "Undercurrents", Charlie decodes some I Ching hexagrams into numbers, but can't work out the next step until Amita adds some brackets to turn it into a phone number.
  • Speak in Unison:
    • When David and Colby are caught in a shootout along with resident Conspiracy Theorist Roy McGill:
      McGill: This is just like Waco!
      David and Colby: Shut up!
    • In "Sneakerhead", David and Liz encounter two of the involved individuals (a foreign consul and a famous rapper) arguing about a pair of $250,000 sneakers that were recently stolen. When Liz reveals that they found one of the sneakers on the foot of a dead perp, the two arguers exchange a horrified look and say together:
      He wore them?! THAT LOWERS THE VALUE!!
  • Spiky Hair: Don has variations of this throughout the series.
  • The Spock: Dr Fleinhart. Charlie doesn't qualify, as he emotes just fine.
  • Spoiler Cover: The first few episodes of Season 5 involve a secondary arc of Charlie trying to get his security clearance back after losing it in the Season 4 finale; without it, he can't work for the FBI (which would necessarily diminish his role in the series). Charlie features prominently on the cover of the Season 5 DVD set.
  • Spoiler Title: One episode is entitled "The Fifth Man". At the beginning of the episode, Charlie's analysis of a robbery crew indicates a four-man team. When the team arrives to stop the robbery, guess what - or rather, who - they get surprised by?
  • Spotting the Thread: In "The Running Man", David gets suspicious of a suspect named Ron Allen when he keeps invoking his rough childhood to the point where he's practically bragging about it, something that David knows from personal experience one usually puts their distance from when one gets a better life. This prompts him to do a deep background check on the suspect, and he discovers that the real Ron Allen died in infancy.
  • Standard Cop Backstory: The show has a few.
    • Megan Reeves was wealthy, but her father resented her because she was born a girl when she was his last chance to have the son he wanted, and it's hinted (but never confirmed) that there's more to the story. Whatever did happen, it was bad enough that she left home when she was 16 and didn't speak to him for over a decade.
    • David Sinclair grew up in a poor neighborhood "dodging gangs just to get [his] high school diploma". His father died when he was in his early teens, and one of his best friends was killed in a random act of violence (for which another friend was unfairly blamed).
    • Colby Granger's father died in a single-car wreck when he was fifteen. There's no way to be sure, but Colby has always suspected it might have been a suicide. He also spent several years in the military.
    • Recurring character Ian Edgerton also has a military background; the rest of his backstory is a complete unknown.
    • Notably averted with Don. Charlie's being a prodigy caused a few small issues, but he was always loved and cared for. There's a reason that he's still so close with his family. He does have a few failed relationships, but that's implied to be mostly by choice.
  • Stating the Simple Solution: In the episode "Hot Shot", Colby watches Megan analyze a victim's whole room, deduce her personality, and finger a potential suspect in her ex-boyfriend. Then he holds up his phone and tells her that David figured out the same thing by talking to the neighbor, but it was fun watching her work anyway.
  • Stealth Hi/Bye: The specialty of mysterious government Agent Floyd (minus the "Bye" part), to the annoyance of Amita: "Stop materializing out of thin air!"
    • Cold Sniper Edgerton also has a habit of doing this, but, then again, he is a sniper. He made a surprise appearance at the end of Season 6, then asked why he wasn't invited to Charlie and Amita's wedding that was planned in one day.
  • Stealth Pun: Possibly the name Eppes constitutes one. Amita: "Charlie, wonderful news! You are now father of an...Eppesilon!" (Don't Explain the Joke mode: Famous mathematician Paul Erdős was known for calling children "Epsilons". It's derived from the Greek letter epsilon being standard use for the arbitrarily small quantity in the definition for the continuity of a function).
  • The Stoic: Don.
  • Stop, or I Shoot Myself!: In the episode "7 Men Out", Granger is getting ready to get one guy when the guy put a gun to his own head. Granger ordered him drop the gun and the guy did. He tossed the gun at Granger and ran for it.
  • Stop, or I Will Shoot!: Colby does this in one episode, telling a fleeing suspect to "stop or I'll shoot you in the back". After he surrenders, Colby admits he had no intention of actually shooting: "I just did not feel like chasing you". Notably, he never does it again, suggesting he may have realized, or been told, that this was not acceptable (this was very early in his time with the FBI).
  • The Storyteller: Charlie Eppes teaches math with stories. He would be great to have as one's professor.
    • Larry indicates that he gets amazing class evaluations.
  • Straight Gay: Amita's parents arrive with a (male) childhood friend of hers, clearing trying to match them up. He appears to be courting Amita throughout the episode. A jealous Charlie finally confronts her, and she tells him that the friend is gay. Lampshaded when an exasperated Charlie asks, "How was I supposed to know that? Do your parents know that?"
  • The Strategist: Charlie would probably qualify with his ability to mathematically predict the moves of evildoers.
  • Straw Vulcan: Usually averted.
  • Successful Sibling Syndrome: Don often felt overshadowed by his genius brother Charlie when they were kids, especially when Charlie (five years younger) ended up joining Don's class in school and graduated with him. Don still has some of this at the beginning of the series, though it gradually disappears as they learn to work together.
  • Suicide by Cop: Buck Winters demands this of Don, feeling like he Must Make Amends for selling out his wife to the Jack Bauer Interrogation Technique, leading to her death at Don's gun. Don, with his new faith, refuses to give it to him, and in the end, Winters loses his nerve and has a sobbing Villainous Breakdown while being dragged away.
  • Super Ringer: In the episode "12:01 A.M.", the CalSci basketball team, which hasn't won in years, is being coached by Prof. Fleinhart, who has a serious problem with losing. He brings in two NBA players as ringers, promising them a ride on the space shuttle. They get a ride on the shuttle simulator in a later episode.
  • Surprise Checkmate: At the end of "Manhunt", Don and Alan team up against Charlie, who thinks nothing of grading his students' papers while they play. When Don points out that Charlie misspelled "anomaly," Charlie gets indignant, and he sticks to his guns over the next few moves, even when Alan reminds him that he's not infallible. Eventually, Don gets the dictionary, and before Charlie can collect his wits, Alan delivers checkmate. Admittedly, this is what it takes to beat Charlie at chess: two people playing him at once and a distraction.
  • Surprisingly Realistic Outcome:
    • In the pilot episode, no less: Charlie uses his mathematical skills to determine the general area where a serial killer lives based on the locations of his murders, but the FBI fails to find a single viable suspect in the target area. When the FBI finally catches the guy, it turns out that he used to live in the target area, but had moved away prior to the beginning of the episode. No matter how good your math is, there will always be some variables that you can't account for.
    • In Cover Me, Charlie gets the idea to stop a new drug from hitting the streets by interrupting the supply chain. In the end, his plan succeeds and that particular drug is contained, but other drugs just surge to take its place. Don tries to reassure him that he still made a difference, but Charlie is less than convinced.
  • Suspect Is Hatless: In the series finale, Don's gun is knocked down from its holster when he's knocked down while making an arrest, and someone else picks it up before he can. The next scene begins with Colby relaying a report.
    Colby: So, LAPD has a couple bystanders who say they can describe the guy. [pauses, his expression implying it's unhelpful] He was Caucasian, medium build, brown hair.
    • They don't get the guy (though they do eventually track down the gun).
  • Suspiciously Similar Substitute: Twice, and both times it has been the female FBI team member. An interesting example because while Megan shares characteristics with both the character she replaced (Terri) and the character who replaces her (Nikki), Terry and Nikki don't have much in common at all, it's just that Megan has very strong attributes that correspond with both. With Terri and Megan the trope comes into play as they're both The Profiler; with Megan and Nikki it's more about the Action Girl aspect.
    • Not sure about Terry, but Diane Farr (who played Megan) was pregnant with twins at the time she left.
  • Sword over Head: "End Game" involves a three-way conflict between the FBI, returning vigilante and ex-Marine Clay Porter, and the criminals that kidnapped Porter's family to get information about a hidden money cache out of him. After Porter's father is killed and Porter decides to cooperate with the FBI (agreeing to confess to his earlier crimes if they save his sister), the climax ends with Porter getting the Big Bad's gun and holding him dead-to-rights while the SWAT team points guns at both of them. Though Porter is dead-set on revenge, Don convinces him to lower the gun, but the villain decides to get in the last word.
    Big Bad: See you in Leavenworth.
    Clay Porter: [shoots him in the leg, drops gun] That's so I can hear you comin'!
  • Sympathetic Murderer: While it doesn't excuse their crimes, a lot of the killers do have sympathetic motives.
    • The one who caused domino-effect killings (he shoots at Gang A, who retaliates against Gang B, who retaliates back, people get caught in the crossfire...repeat until about 150 people are dead) to avenge his young son who was murdered by gangsters. By the time the crew catches up with him, he is very clearly insane.
    • The Knight Templar murderer who targets child molesters in "Killer Chat" turns out to be the wife of a pedophile who had sexually abused the couple's daughter. Despite the brutality of the crimes, it's hard not to sympathize with the killer once the motive is revealed.
    • The killer in "Sacrifice" becomes a lot more sympathetic when we learn his motive: he was from a poor community who managed to leave for a better life, and ended up working for a researcher who was working on a program to mathematically decide which communities have enough "potential" to allocate money and resources to. Knowing that such a program could justify taking money away from poorer, crime-ridden neighborhoods like his own and give it to wealthier ones, marginalizing already-neglected communities, he killed his boss to make sure the program would never see the light of day.
    • One shows up in "Velocity". He was a street racer until he caused a fatal accident, whereupon he swore off it for good. But when some of his old racer acquaintances (who often drove past him to mess with him) caused a crash at one of his hangouts and killed a new friend, he ended up beating the one responsible to death. That's the sympathetic part; the part where he mistook a 17-year-old passenger for the driver and kicked him in the head so hard he put him in a coma, less so.
    • In "Thirteen", an ex-army sniper performs Vigilante Executions on the serial killers who tortured and murdered his girlfriend, having tailed the police to find them. It doesn't excuse his actions (both serial killers were in custody, so there was no threat to anyone), but it's almost hard not to sympathize with the guy.
    • The plot of the series finale involves two near-misses on this: a battered woman whose boyfriend keeps violating his restraining order, and a teenage boy whose neighbor has been bullying his family. However, the woman is unable to bring herself to do it, and the other attempt is interrupted by the FBI.
  • Sympathy for the Devil: Larry expresses sympathy for the serial poisoner in "Toxin", saying that although he had good ideas in the beginning and got what he wanted in the end with the shutdown of the pharmaceutical company selling bad drugs, he did so at the cost of his soul. On the other end, Alan laments the shutdown of the company for all the life-saving drugs they could've produced, while looking at a picture of his deceased wife.
  • Take My Hand!: In "Primacy", Charlie has to do this to pull Colby to safety, after the latter is almost washed away by an opening dam gate.
  • Taken During the Ending:
    • Megan is taken by Crystal Hoyle in the Season three episode "Spree", which sets up events in the next episode, events which also set up the rest of season three, especially with Don's actions to get Megan back.
    • Amita is kidnapped at the end of "Greatest Hits" when she and Charlie are leaving CalSci for the night, which leads to the fifth season finale when the team goes up against a cult that is holding Amita.
  • Talking the Monster to Death:
    • Don convinces the last criminal who stole a truck of radioactive cesium to surrender by pointing out that he has contracted acute radiation poisoning, and surrendering is the only way he can get medical attention in time.
    • The climax of "7 Men Down" has David, Colby and Nikki bust into the last round of a Russian Roulette tournament, but all the gang members present and betting on the outcome immediately pull their guns on them. When putting their guns away doesn't defuse the situation, David, knowing the game is rigged, makes a bet himself, but also challenges the second player, who is the one who rigged the guns and had never lost a round, to go first. When he refuses, the gangs realise what's going on and also put their guns away.
  • Tagline:
    • "How do you solve a crime in a city of 8 million? It's all in the numbers".
    • "People lie. Numbers don't."
  • Take a Third Option: In the series's penultimate episode, Charlie and Amita get offers for visiting professorships in Cambridge, in the middle of their wedding preparations, leaving them stuck between either forgoing the professorship, getting married in England with major travel difficulties for their family and friends, or postponing their wedding to even later. In the end, they decide to take the fourth choice: get Larry to marry them tomorrow.
  • Tangled Family Tree: In "Nine Wives", a family tree diagram found in a cult leader's trailer is so convoluted (due to the massive number of marriages each man has, as well as the prevelance of incest within the cult) that Charlie and Amita initially aren't sure what it is, and only figure it out after Millie mistakes it for a cattle breeding chart (which is close enough to "family tree" for Charlie and Amita to finally realize what it actually is).
  • Teacher/Student Romance:
    • Charlie and Amita. He's only her thesis advisor! Really! Less weird in that since Charlie was a child prodigy, they're about the same age. Also, Charlie doesn't begin dating her until after she finishes her thesis, when he's no longer in a position of authority over her.
    • A much weirder and less acceptable example underlies the plot of the Season 3 premiere.
  • Team Dad: Don.
    • Alan, too. And not just in the sense of actually being Charlie and Don's father—he will at times give everybody useful advice or be a sounding board for problems.
  • Tempting Fate: When David and Colby corner a gun-wielding suspect in a garage that was recently used to make bombs:
    David: Sir, you're in a bomb lab! Now you know better than-
    Suspect: AAAAHHH! (Pulls the trigger)
    *BOOM*
    Colby: ...apparently not.
  • Theme Serial Killer: A serial killer whose victims had the same names as the 12 apostles and killed them in the way each apostle died.
    • Not only that but the locations of their deaths were consistent with a map of the last significant events of Jesus's life.
  • Therapy Is for the Weak: After the Crystal Hoyle incident, Don is encouraged to go to therapy, and is initially resistant to the idea before he finally gives in.
  • There Are No Coincidences: Comes up a few times. In this case, Charlie does allow for the possibility of coincidences, but he's also able to see when an apparent coincidence is a little too improbable. In one episode, he realizes that a bus accident was staged due to the sheer number of factors that had to come together at the exact right moment; in a later episode, he uncovers a murder plot after discovering that five people who worked together all died within a few weeks of each other in a series of supposedly random incidents (four "accidents" and one "suicide"), the odds of which, according to Charlie, are about 700 million to one.
  • "The Reason You Suck" Speech: At the end of "Double Down", Larry gives one to an old colleague who, unlike Larry, couldn't stop being The Gambling Addict and got some of his students into the realm of card-counting and beating casinos, which ended badly for all of them.
  • There Should Be a Law: David basically acts like this in "Arm in Arms" toward the legal arms dealer Arvin Lindell, including basically kidnapping him, driving him out to a memorial, and leaving him there.
  • They Call Me MISTER Tibbs!: Dr. Mildred Finch insists on being called Millie. Played for irony, since at the same time she stresses this informality, she's coming down hard on her subordinates in other areas.
  • This Looks Like a Job for Aquaman: Alan sometimes offers his insight on a few of Don's cases, usually relating to his old profession as a city planner.
  • Throw the Dog a Bone: In "Jack of All Trades", the FBI are after a conman that has stolen thousands of dollars from multiple companies. Once they find out that the conman, Kevin Oliver, is only 18 and his main motivation is to find his birth mother, after tracking down the mother themselves and using her as bait to draw him out, Don gives Oliver a few moments with her, over the objections of the Inspector Javert working with them.
  • Tiny Guy, Huge Girl: Charlie and Amita.
  • Title Drop: The show had a combination of episode titles that were pulled directly from elements of the plot and episode titles that were more metaphorical or symbolic (and a handful that were both, eg. "Double Down"), so it's about a 50/50 chance that a title will be dropped in any given episode note . However, pretty much all the title drops that did happen were crafted in such a way that they occur naturally as part of the dialogue and consequently aren't especially noticeable.
    • An interesting variation in "Atomic No. 33". No one actually speaks the title as written, but, "Atomic Number 33" is a scientific reference to arsenic, and arsenic plays a significant role in the plot and is therefore mentionednote  more than a few times.
    • Another variation in "Thirty-Six Hours". No one actually speaks the title (or any variation of it), but with every scene change, there's a title card indicating how many hours into the disaster they are. The final card, predictably, reads "Hour Thirty-Six".
    • The series title itself, being a single word critical to much of the work in the series, is of course dropped countless times, but it is worth noting that it's specifically dropped as the final word of the pilot episode (as part of Charlie's Catchphrase "Everything is Numbers").
  • Title by Number:
    • Sniper Zero.
    • Nine Wives.
    • One Hour.
    • Thirteen.
    • Atomic No. 33.
    • Thirty-Six Hours.
    • The Fifth man.
    • 7 Men Out.
  • Title-Only Opening: The show usually uses a title with Opening Narration over it, but in Season 2's "Harvest", the teaser ended with the titletype appearing on a blank black screen, with the credits shown over the first scene.
  • Torture Is Ineffective: It's almost a throwaway moment, but in the episode "Thirteen", Megan experiences a flashback in which a man is screaming and she's yelling "That's enough! He'll say anything you want!" note  A later conversation with Colby indicates that she was forced to be involved in the torture of detainees suspected of terrorism, suggesting that the memory she was reliving was from that assignment.
  • Torture Technician: Mason Lancer in "Trust Metric" is this to a T. His "weapon" of choice is drug cocktails, and he's quite proud of how well he knows his way around them. he also keeps the cool, detached interest, never breaking a sweat, saying everything like it's an idle curiosity. It's not until the FBI boards the boat that he starts to look at all worried, and even then he remains calm and methodical as he prepares to kill Colby. (Luckily, he doesn't quite succeed).
  • Trailers Always Spoil: The promo for the episode "Spree" made a big deal about Megan being kidnapped, as if the entire episode was about that. Almost none of the scenes in the promo are in the episode (they're in the next one, "Two Daughters"), and Megan isn't kidnapped until the last thirty seconds of the episode, as a cliffhanger.
  • Treacherous Advisor: Some episodes have certain advisors, from arson experts and anti-terrorism experts to ordinary comic book experts, helping the FBI with their case, but who turn out to have orchestrated the case themselves for whatever reason.
    • Subverted in "The O.G.". The guns used to orchestrate several shooting chains between gangs turned out to have all come from a gun buy-back program and all signed off by Lieutenant Gary Walker, who was advising the team up to this point, however as Walker points out, his signature only means they were turned in at his drop-off location, and there were other people involved with the program who would also have had access to the guns.
    • Played with in "Scratch" via a Bait-and-Switch; it's initially thought that the lottery expert working with the team is the inside man, but later it turns out that it's the expert's boss that's the inside man.
  • Turn to Religion: The Eppes family are non-observant Jewish, but in "Scan Man", after Don has an agent gunned down in front of him (complete with a Fatal Family Photo), he decides to delve deeper into the faith and goes to a synagogue at the end of the episode. This faith helps him through a few other crises like the one in "Arrow of Time".
  • Ultra Super Death Gore Fest Chainsawer 3000: The show actually avoided this trope in "Primacy" when they did an Alternate Reality Game with a video game component that stuck to fairly standard fantasy violence. And they ran ran the game as an actual alternate reality game. And the show wasn't an Author Tract about video game violence. And on the whole it was pretty cool.
  • Unbroken Vigil: In "The Fifth Man" Alan does this when Don is in the hospital, while Charlie wanted to do the same but Alan told him and the FBI team that Don would want them to work on the case but Charlie does visit in between working the case.
  • The Un Favourite:
    • Don has moments where he seems to believe this; it's largely implied that the amount of energy and attention Charlie's Child Prodigy status required meant that Don often ended up not getting as much as attention he should have had (including the fact that his mother moved to Princeton with Charlie to support him). However, his father makes it clear that, while he knows Don got the short end of the stick, it was never intentional, he regrets it, and he loves Don every bit as much as he loves Charlie. (Depending on how one reads certain scenes in "Hot Shot", it can possibly be said that his note  mother feels the same way).
    • Megan implies she felt like this as well, largely due to the fact that she disappointed her parents just by being born female. Additional details about her childhood and her relationship with her father seem to reinforce this.
  • Unfriendly Fire: the episode aptly named "Friendly Fire" reveals that Don's mentor is a Dirty Cop who used a shootout as a cover to kill a member of his own team after finding out he was an Internal Affairs informant, and then killed a second agent because he witnessed the first murder.
  • Unit Confusion: Occurs in-universe in "Thirty-Six Hours" when Charlie gives Colby a series of very precise directions to get into the wreck but (potentially because he's been awake for well over 24 hours straight by this point) forgets to specify unit of measurement; he means them in meters but Colby counts them out in yards, causing him to run into a dead end. Once it becomes clear that there was a mistake somewhere along the way, Charlie figures it out fairly quickly, and it ends up being little more than a minor inconvenience.

     V-Z 
  • Verbal Backspace: In one episode, the initial suspect in the bombing of a philanthropy organization is a nutty conspiracy theorist who claims the group isn't on the up-an-up. When a deeper look suggests the organization might actually have something to hide, Robin attempts to suggest that the conspiracy theorist might have a point for once, but it doesn't quite come out right intially.
    Robin: McGill may not be so crazy [Beat] He's crazy. But that doesn't mean that he's wrong.
  • Video Arcade: In the Pilot, Charlie and Larry meet in an arcade on campus on CalSci, where Larry gives Charlie some advice on the current case, while simultaneously getting a high score on his current game.
  • Vigilante Militia:
    • "Frenemies" features a vigilante group called Vanguard made up of college students trying to take down Vic Tooner, an infamous local crime lord who remains free even after multiple police investigations. Several of them are motivated by Tooner's rape and murder of a girl several of them had classes with (and whom their leader was in love with), while others are drawn in by the leader's charismatic arguments about making a difference to the community. They use their leader's hacking skills to eavesdrop on Tooner's conversations and either film Tooner's men committing crimes or ambush them at crime scenes with flash bombs and leave the goons tied up for the police. The group uses military tactics and codenames, with many of them not knowing who the others are. The Victim of the Week is a Vanguard member who Tooner kills in retaliation for their activities.
    • In "Killer Chat," an investigation into the murder of several pedophiles leads to a group called Parents Stop Predators, who pose as underage girls on chat rooms and try to get pedophiles to arrange to meet the nonexistent underage girls for sex. When they succeed, they turn over their evidence to the authorities. When the pedophiles avoid doing anything actually illegal, the vigilantes urge them to seek counseling and warn the pedophiles' families about their actions.
    • In the series finale, Don's service weapon is stolen and used by various people who know each other from online chat rooms venting about their problems with local criminals (a community watch member who's been unable to stop some drug dealers legitimately, a woman being stalked by her ex, etc.) As soon as one person uses the gun to kill a criminal (or decides not to use it after all), they pass it on to someone else.
  • Villain Has a Point: The victim in "Sacrifice" was killed because he was developing a computer program that would have allocated educational resources based on a mathematical assessment of "potential" (or as Don puts it, it's a justification to take money away from poor communities and make sure only the wealthy got opportunities). His assistant, Scott, grew up in a poor crime-ridden neighborhood, and knew that such a program would have denied him the opportunities that allowed him to escape for a better life. He also knew that other people like him would be denied any opportunity for a better life if the program were ever implemented, so he killed his boss. Once he's arrested and explains his motives to Charlie, Scott compares what his boss was doing to the Nazis using the Theory of Eugenics to justify murdering the poor and those that they had deemed "undesirable", as both programs would take somebody's chance of life away due to factors beyond anybody's control. At the end of the episode, Charlie destroys the victim's work so nobody can take advantage of it even though he refuses to condone the murder.
  • Villain's Dying Grace: Dawyne dies saving Colby's life.
  • Virtual Danger Denial: A Playful Hacker cheerfully pisses off a number of powerful agencies online, legal and illegal, and is in total denial that they could come after him in real life. At least until it gets one of his loved ones killed.
  • Vulnerable Convoy: Colby escapes his convoy with his cuffed partner, Dwayne, ridiculously easily in the fourth season premiere.
  • Waiting for a Break: Brought up in Hollywood Homicide, as the victim was someone who was trying to to break into Hollywood and was working as an escort while trying to do so.
  • Walking the Earth: Larry is always doing this or wanting to.
    • Except when he went into space.
    • Then when he went into the desert.
  • Water Source Tampering: One episode involves a terrorist plot to put sarin gas into the Los Angeles water main. Not only would this kill anyone drinking the water, but also anyone taking a shower, doing the dishes, or being in the vicinity of sprinklers.
  • The Watson: AKA the FBI, as the ones who constantly prompt Charlie and the other math experts to explain their reasoning.
  • Wedding Finale: The sixth season (and series) finale had Charlie and Amita's wedding.
  • We Hardly Knew Ye:
    • Agent Adam McKnight, who is killed at the beginning of the second episode while the team is trying to stop an armed robbery, and is mentioned again a season later when Don is trying to console Megan when she loses an agent during a raid.
    • Terry Lake (Sabrina Lloyd) disappears towards the end of the first season and the second season premiere states that she moved back to Washington D.C. to work things out with her ex and is hardly mentioned again.
  • Welcome Back, Traitor: In the season three finale, Colby is revealed to be a spy for the Chinese in the FBI. While next season's premiere reveals it wasn't quite true, he IS and always has been a plant by the Department of Justice, and returns to the FBI office with a few hiccups.
  • "Well Done, Son" Guy: Don has moments of this, especially early on in the series, though it's clear from an outsider's perspective how much his father loves him. It's pretty strongly suggested that the amount of attention his parents devoted to Charlie's genius has led Don to believe (wrongly) that he's The Unfavorite.
    • Colby also seems to be this with Don, especially when he feels like he's let Don down. Just look at the smile on his face in "Thirteen" when Don calls him "brother" and tells hims he's approved his request to stay.
    • Megan also suggests that she was once this with her father. Unfortunately, it seems he never did give her the validation she craved, leading to a lot of hurt and resentment.
  • Well-Intentioned Extremist:
    • The scientist who intentionally infected people with Spanish Flu to prove that the pharmaceutical companies chose the wrong (less virulent) strain to use in the development of vaccines and treatments, because he was convinced that a real epidemic was only a matter of time and so getting it right was literally a matter of life and death.
    • The Homeland Security agent who saw vulnerabilities in counter-terrorism operations that had to be patched, and tried drawing attention to them by using a deadly gas in one of them (watered down to prevent casualties). When that didn't work, he planted a (fake) bomb on his boss to make him feel the fear of soldiers saddled with ineffective strategies and protections.
    • The Knight Templar Serial Killer in "Killer Chat" who targets child molesters so no kid would ever be hurt by one again after her husband molested their daughter.
    • The man who started killing gang members in such a way as to maximize retaliations, with the intent of getting as many gang members as possible killed off, after his son was killed in a gang war.
    • The narcotics cop who was feeding a gang member the locations of rival gangs' stash houses so he could raid them, figuring that fewer drug dealers was better for the community. He crosses the Moral Event Horizon when the gang member decides he's had enough and wants to come forward; he arranges for the gang member to go down in a raid, and then kills the rookie cop who pulled the trigger when he starts to piece together that something wasn't right and was about to go to Internal Affairs with his suspicions. As Don hauls him off, he keeps hollering to Lt. Walker that his murdered colleague wouldn't listen to reason and that he had no choice but to kill him.
    • The Neighborhood Watch types who got ahold of Don's gun used it to kill a pair of drug dealers who sold to schoolchildren and a serial drunk driver who ran down two people, and to intimidate a vicious neighbor who turned out to be an escaped murderer.
  • Western Terrorists: A bomb explodes in front of an army recruiting office, which is discovered to be built similarly to a bomb that went off during a Vietnam War era attack on an ROTC office. The bomber is the son of a former member of an anti-war group, and it's revealed that Alan was also a member of the group.
  • We Used to Be Friends:
    • Colby Granger and Dwayne Carter were close friends in Afghanistan, but then after they got home, Carter defected to the Chinese and tried to get Colby to do the same. For his part, Colby pretended to go along with it in order to figure out who Carter was working for.
      • The rest of the team has this when it appears Colby is a traitor, especially when they're assigned to track him down after he escapes custody. Megan is devastated, David is enraged, and Don is upset that he could have missed something so significant. To a lesser degree, David continued to feel this way even after the truth is revealed. (He gets over it, but it takes a while).
      David: I still don't know who he is. I didn't know him when he was a spy, now he's some guy who pretended to be a spy. Pretended to be my partner.
    • In "Friendly Fire", Don finds out that his mentor, Pete Fox, orchestrated the death of two cops to cover up Fox's own corruption. Needless to say, he's devastated.
  • Wham Line: From the Season 3 finale, "The Janus List". The entire episode has been about getting a list of double agents, not because they were seeking the list itself, but because its author is setting off bombs in a roundabout way, to make Charlie and Don prove they were worthy to receive the list. They figure out the clues, stop the bombs, and listen to the list...
    Janus List: Colby Granger, FBI, also working for the Chinese.
    • In the following episode, "Trust Metric", Big Bad Lancer gets one when he has Colby on the freighter:
      Lancer: That's a question I need answered, Agent Granger.
      Colby: Oh, it's not "Agent" anymore.
      Lancer: Mike Kirkland * says differently.
    • A more personal example in "One Hour", when Don's therapist finally goads him into revealing the extent of his trust issues. It's as much of a Wham to Don himself as anyone, since even he hadn't been consciously aware of how bad his problem was.
      Don: Look, I'm their boss! I don't have to trust them; it's their job to trust me!
  • What Does She See in Him?: At the end of "Toxin", Absent-Minded Professor Larry hints at a potential budding romance between him and Megan Reeves, and gets a bit huffy when the Eppes men start joking with him about it. Colby, David, and engineering professor Ray Goleski have all also discussed the unusualness at some point.
    Charlie: Megan?
    Don: And Larry.
    Alan: Now there's an image.
  • What Happened to the Mouse?:
    • At the beginning of Season 2, a prosecutor named Nadine was set up as a potential love interest for Don. She shows up twice more and then disappears and is never so much as talked about for the rest of the series.
    • The season 5 episode "Animal Rites" teases a possible budding relationship between Larry and another professor named Lorna. Lorna is never seen or mentioned again.
  • What the Hell, Hero?:
    • "Backscatter" has Don and Lt. Walker exchange these when Don tries to keep Charlie off a case where the Russian Mob directly threatened the Eppes family, only for Charlie to approach Walker with a "Eureka!" Moment behind Don's back. Don is angry that Walker helped bring Charlie back into the case, while Walker admonishes Don for backing off instead of using every resource at his disposal (including Charlie) to beat the Mob.
  • Who Murdered the Asshole:
    • The series finale features the murders of two drug dealers and a dangerous drunk driver (who were assassinated with a Glock stolen from Don, an error that could get Don fired, and then passed along to a chain of wanna-be vigilantes). The motives are so numerous that they have to turn to social media to identify the killer of the drug dealers, and they never do find out who killed the drunk driver.
    • A non-murder example the third season episode One Hour when the son of a controversial music producer is kidnapped. When Colby tries to ask the father if he has any enemies, the man suggests he "pick up your mugbook and pick a page". (Fortunately, some later hints dropped by the kidnapper give the team the information they need to zero in on a suspect.
  • Who's on First?: In one episode, one of these is set up, but Nikki stops it before it gets started.
    David: Who was Wattsnote  busting if there wasn't anybody out here to bust?
    [[Cut to]]
    Colby: Otter killers.
    Don: Ought to what?
    Nikki: Don't. We did the Marx Brothers thing already.
  • Who Shot JFK?: In the fifth season episode "Conspiracy Theory" a subplot deals with Colby and David arguing about who shot at Kennedy with David bringing up theories and Colby dismissing them. By the end of the episode they try to get Alan to referee, but Alan gets them to cut a truce and get over the issue, having seen this sort of argument break up another friend group.
  • Who Would Want to Watch Us?: In the episode "Graphic", after Don and Charlie have returned a rare comic to its artist, said artist begins drawing them and suggests a complete comic series about an FBI agent and his Mathematician brother. Cue Don's line of "Aw, no-one would believe it."
  • Will They or Won't They?: Charlie and Amita.
    • They do: They got married.
    • And Don and Robin. In the final episode, they get engaged.
  • Working with the Ex: Between fellow FBI agents Terri and Liz, federal prosecutor Robin, and even one-off characters like a counterfeit specialist from the Secret Service in one episode and an ATF agent in another, Don runs into a lot of his Old Flames throughout the job.
  • Would Hurt a Child: The FBI deals with child kidnappers, pedophiles and violent offenders throughout many episodes, but one that takes the cake is "Waste Not", where a company responsible for paving low-income school playgrounds also "disposed" barrels of toxic waste underneath them that eventually leaked and, in addition to turning the school into a cancer cluster, caused a sinkhole that trapped several kids, caused chemical rashes, and even killed a teaching assistant.
  • Wouldn't Hit a Girl: In "Arrow of Time", Nikki and Colby go to arrest a person escapee's girlfriend - a rather large and strong woman. She gets the upper hand on Colby rather quickly and he's not helped in the slightest by his small-town-values reluctance to hit back. Nikki, whose life experience is somewhat different, finds the whole thing hilarious.
    Colby: A little help here?
    Nikki: Punch her!
    Colby: [indignantly] She's a girl!
    Nikki: "Girl" must mean something different in Idaho. (clocks her with a 2x4)
  • Wouldn't Hurt a Child: Both invoked and played out in "The Art of Reckoning". A hitman on death row tells the FBI a story about how he murdered a young child, but the evidence doesn't support it. As he stubbornly sticks to his story, Colby wonders whether the hitman was unable to kill the child and hid him away somewhere instead. They eventually find that the memory was so horrible that he had repressed it, fabricating a memory in its place. When he finally remembers what really happened, it's a less pleasant revelation: the hitman was, in fact, unable to make himself kill a child, so his client ended up doing it himself. The fabricated memory was an attempt to create a reality in which the child's last moments were less horrific, even though the false memory put the hitman himself in a worse position.
  • Writer on Board: The eco sub-arc, the season finale about treatment of minorities from "risky" areas of the world.
  • Writers Cannot Do Math: Zigzagged like crazy.
  • Written-In Absence: Done repeatedly.
    • When MacNicol took a temporary leave of absence during the third season to be in TwentyFour, Larry (a professor of Cosmology) spent six months on the International Space Station. Since the showrunners knew about it well in advance, they wrote in a several-episode build-up to the launch.
    • In the same season, Diane Farr (Megan) took a temporary leave of absence because she was pregnant. This was written into the script as Reeves being forced into a special assignment, which would form the basis for much of her character arc in Season 4.
    • This escalates to the point of ridiculous in the last two seasons, as due to budgetary concerns, it was too expensive to have as many series regulars as they had appear in every episode, so it became common for only three of the four supporting FBI agents (David, Colby, Liz, Nikki) to be present at a time. This is usually given a Hand Wave or completely ignored, but it does get lampshaded in "12:01 AM" (with Colby Granger (Dylan Bruno) being the absent character in that episode).
  • Wrong Genre Savvy: In the pilot episode, no less: Charlie uses his mathematical skills to determine the general area where a serial killer lives based on the locations of his murders, but the FBI fails to find a single viable suspect in the target area. When the FBI finally catches the guy, it turns out that he used to live in the target area, but had moved away prior to the beginning of the episode. No matter how good your math is, there will always be some variables that you can't account for.
  • You Meddling Kids: Said at the end of an episode, in which Don, his team, and Charlie investigate spooky activity at a supposedly abandoned airbase. This is more of an inversion, thought, as it is very ambiguous whether the person that said it was a villain at all, and he had helped them solve the case. He is also very wacky, talked in an invisible cell phone and appeared out of thin air. He also called three professors and an FBI agent meddling kids.
  • You Said You Would Let Them Go:
    • In "Backscatter", two bank employees are kidnapped to force their boss to facilitate a heist. When Don and Gary Walker are trying to convince the boss to help them, one of the things they tell him is that no matter what the guy claims, the hostages are pretty much guaranteed to be killed as soon as they're no longer needed.
    • In "One Hour", two bodyguards who had been involved in a conspiracy to kidnap their charge are shot, one fatally. When the agents confront the survivor with evidence he was in on it, he points out that if they're willing to kill their accomplices, "You gotta figure they don't plan on leaving that boy alive." This is later confirmed; when Colby makes the ransom drop and rescues the boy, the kidnapper is seen trying to set up a shot before David comes in and arrests him.

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