Innocuously Important Episode / Live-Action TV

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• Two episodes from the first season of Angel feature flashbacks that delve into Angel's backstory, paralleling the episodes' events in the present. The flashbacks from "The Prodigal" focus on Liam's bad relationship with his father before and after he was sired, in an episode that gave focus to Kate Lockley's relationship with her own father. Those from "Five by Five" recount Angel's whereabouts slightly before and after getting cursed with a soul, mirroring Faith Lehane's quest for redemption which starts at the episode's end. But more importantly, the flashbacks introduce (or reintroduce) the audience to Darla, a probably long-forgotten character from the parent show, slain a few episodes in, who is then resurrected in the season finale and becomes very important to the show.
• Babylon 5. Several episodes of the first season.
  • The thirteenth episode "Signs and Portents". The episode's "A" plot is some fairly standard and unimportant thing involving Raiders [space pirates] and a Centauri artifact called The Eye. The "B" plot, involving the first appearance of the enigmatic Mr Morden and the question "What do you want?", turns out to be incredibly important and crucial to the rest of the series — but the episode's retrospective importance only kicks in at the first season finale.
    • Its importance was lampshaded by the fact that the entire first season was also named "Signs and Portents" (though a casual viewer wouldn't know this - the season titles only appeared on fan sites.) "Portents", of course, are hints about future events.
    • The A Plot does have one rather important thing happen in it: it's the first appearance of The Shadows. They even get name dropped, but in a way that most viewers would dismiss as unimportant on a first viewing.
  • "Midnight on the Firing Line" is the former Trope Namer. The first episode after the pilot movie, it featured subplots and character moments that the show kept referring to throughout many of its best moments over the rest of its run.
  • "Infection", the fourth episode of the show, managed to introduce several elements that would become very important later on, including Interplanetary Expeditions, ISN, Earth's desire for advanced biotechnology and the first mention of previous Shadow War a thousand years ago - and certain revelations about Sinclair's past and how it drives his behaviour in the present. Not bad for what is almost universally considered to be a lackluster Monster of the Week episode.
  • The second episode of season 2, "Revelations", has an obviously important A-plot involving G'Kar, Garibaldi and Delenn in particular – and also a B-plot featuring Sheridan meeting his sister and coming to terms with the death of his wife Anna after getting a last message from her. The B-plot seems like little more than a bit of character development for the new guy, but Anna Sheridan will turn out to be incredibly important to one episode later in this season, and even more important the last few episodes of the next.
  • The A-plot of "Grey 17 is Missing", the 19th episode of season 3, is some silliness involving Garibaldi investigating a sealed-off Missing Floor in the station's Grey Sector. The B-plot, however, involves Delenn becoming the new leader of the Rangers, which is very important to the Myth Arc of the show. It's also the beginning of Neroon's path to redemption, which culminates the following season.
• The Battlestar Galactica first-season episode "Tigh Me Up, Tigh Me Down" was thought to be a comedy filler episode (the only intentionally comic episode in the entire show) revolving around a series of misunderstandings between Ellen Tigh (who unexpectedly reappears in the fleet) and Commander Adama (who believes Ellen is a Cylon sleeper agent). The whole episode climaxes in an amusing scene where everyone humorously works out their differences, and the matter is resolved. Three seasons later, in "Sometimes A Great Notion", it turns out this episode set up the eventual arc and reveal that Ellen was the final Cylon.
• Better Call Saul:
  • "Coushatta" seems like a Filler or Breather Episode, but it's actually important to the series since it reveals what all of Gus Fring's plans for Nacho have been building up to and it reveals Lalo Salamanca showing up to take control of the gang, plus notably, Kim Wexler's Face–Heel Turn (on a sliding scale of evil, not that evil yet, but still, a grifter).
  • The Kettleman subplot in season 1 may have seemed like filler at first to establish the kinds of clients Jimmy takes on. But it's what first gets him into business with Nacho (albeit unwillingly). His relationship with Nacho is ultimately what gets him involved with Lalo, Gus, and the cartel, driving the rest of the series. It also represents the first time he's pressured to help plan a crime, rather than just defending criminals after the fact.
• Breaking Bad:
  • "Gray Matter" has a meeting with Walt's close friends from college, Elliot and Gretchen Schwartz who try to offer him a job, which Walt refuses due to his pride. This will be extremely important later, as Walt's true reason for continuing to cook meth is related to the said friends, as well as both Elliot and Gretchen becoming the only ways Walt can safely handover rest of his money to his family.
  • "Negro y Azul" has the A-plot being Walt and Jesse dealing with the fallout of Spooge's death at the hands of his wife, but this episode introduces Beneke Fabricators as well as the Cartel. Skyler ends up having an affair with her boss Ted Beneke after she finds out about Walter's meth cooking in Season 3, and one of the major factors in the resolution of Season 4 is Beneke's cooking of his company's books and Skyler's work to cover it up. As for the Cartel, Tortuga's killers in this episode become major antagonists in the next season, and their deaths lead to Gus Fring slowly taking over the Cartel.
• Buffy the Vampire Slayer.
  • "Killed By Death". Buffy is sick and ends up in hospital - a place she hates since her cousin died in a hospital when they were children. While the Monster of the Week in the episode (which was also responsible for her cousin's death) is dealt with, Sunnydale General ends up playing a big role in Season Five - not only does Buffy's mother Joyce end up with a brain tumor and spends a few episodes there, but we're also, at the same time, introduced to the character Ben Wilkinson, a young medical intern who serves as a possible Love Interest to Buffy and who turns out to be the mortal, human shell of Glory, the Big Bad of Season Five - Glory's plans, in turn, result in Buffy's death in the Season Five finale.
  • "Amends" was just a liked but relatively low-key little Christmas Episode from Season 3... but you'll need to remember it to understand the machinations of the Big Bad come Season 7.
  • "The Wish" is an Alternate Reality Episode that introduces Anyanka, a Reality Warping demon who Does Not Like Men. While the episode is darker and has higher stakes than normal, by the end everything gets reset - the alternate timeline is erased, noone remembers it, and Anyanka is trapped as a human teenager and can no longer do any harm. Despite this, Anyanka (called Anya while in human form) actually becomes a recurring character and eventually part of the main cast, reluctantly bonding with Xander due to him being less unlikable than most men and occasionally using her knowledge of demons to help the gang out.
  • "I Was Made to Love You" on several accounts. This episode (and earlier, "Ted") seemed a bit out of place at the time of airing (robots? really?) but set up the suspension of disbelief needed for the Buffybot to exist, which allowed Dawn to stay in Sunnydale after the events of "The Gift". This episode also introduced Warren, who would become a major villain in the following season. And lastly, while most of the episode is a fun romp with a tone somewhat on the lighter side for the series, the final scene sets up the major Wham Episode to follow.
  • In "Something Blue", Willow loses herself in magic as a way of dealing with Oz's absence and hijinks ensue, one example being Buffy and Spike making out passionately in what is viewed as an in-universe Crack Pairing. Things appear to be neatly resolved at the end of the episode, but both Willow's strong emotional reaction to the loss of a significant other (resulting in a misuse of her magical abilities) and the Buffy/Spike romantic chemistry are things that will pop up again in Season 5 and become prominent features of Season 6.
• The Charmed season 2 episode "P3H20" has the trio meet their mother's old Whitelighter Sam Wilder, who helps them deal with the water demon who killed their mother at the cost of his own life. During the episode, Sam mentions that he and their mother were in love with each other, paralleling Piper's own relationship with Leo. This allowed the show to bring in Paige Matthews as the result of the affair and a replacement for the Charmed Ones sisterhood following Prue's death in the season 4 premiere.
• Community delighted in these; many of its one-off genre spoof episodes dropped important plot points that would later prove to be very important to the show's ongoing story. To name a few examples:
  • "Epidemiology" is a Halloween Episode parodying zombie movies, but it also features Chang and Shirley briefly sleeping together during a moment when they think they're going to die. A few episodes later, Shirley discovers that she's pregnant shortly after getting back together with her ex-husband Andre, leading to a running mystery over whether Chang might be the father of her child—which isn't resolved until the season finale.
  • "Contemporary Impressionists" (the one where Abed blows all his money hiring celebrity impersonators) almost singlehandedly sets up the entire multi-part finale of Season 3. The episode's climax involves the study group getting roped into acting as celebrity impersonators for a teenager's Bar Mitzvah—where Chang (who's been forced to become a security guard at Greendale) gets the idea to hire the kid's friends as a private army of child soldiers, and to hire a Moby impersonator to impersonate Dean Pelton. He ends up using his child army to take over Greendale and secretly replace the Dean with the impostor, forcing the study group to free Greendale from his tyrannical rule.
  • Relatedly: "Basic Lupine Urology" is a goofy Law & Order parody that mostly revolves around the study group trying to figure out who destroyed their science project, but the episode's events also end up leading directly to the season finale. When the study group suspects that Star-Burns may have done the deed, they break into his locker and inadvertently expose the fact that he's been running a meth lab out of the trunk of his car, which leads to him faking his death to avoid legal scrutiny. Soon after, the study group's science professor abruptly resigns from the school due to feeling responsible for Star-Burns' "death", forcing them to make up their incomplete science grade in Summer School—which leads to them delivering angry speeches at Star-Burns' memorial service and accidentally causing a riot, which Chang uses as a pretext for taking over the school. Damn.
• Doctor Who:
  • "The Daleks" was initially written as a space adventure story based on 1950s sci-fi serials, with anti-war themes and some quirky Nazi-like "bug-eyed monsters" as villains. Due to the extreme popularity of aforementioned villains, it is now impossible to watch the story without being aware that this is the Doctor's first encounter with his single most enduring nemesis.
  • "The Rescue" seems like a simple storyline on the face of it, as the TARDIS materialises on the planet Dido, exposes the man responsible for killing most of the natives, and departs with a new companion. However, it is notable as the first time the Doctor and his companions explicitly stay until they have righted an injustice because they want to do so; on prior occasions the travellers were forced to remain because they were separated from each other or the TARDIS was inaccessible for some reason, but there is never anything stopping the Doctor, Ian and Barbara just taking off (on their own or with Vicki) once they learn about Koquillion.
  • "The Tenth Planet" has three main points about it that get very important later. It introduced the "Base under Siege" formula that would dominate Troughton's tenure and influence the show's slide from a Genre Roulette format into Monster of the Week, introduced the Cybermen (though they were given a soft-reboot a few episodes later), and ended with a shock twist of the Doctor suddenly turning into a totally different actor. All of these at the time were just decisions being made for that particular episode and Real Life Writes the Plot, but due to Who's Kudzu Plot nature all became very significant (although some in terms of the show's feel rather than in plot points).
  • "The Web of Fear" was intended at the time as a sequel to an earlier story about the Doctor teaming up with the military and a now-older ally to fight killer robot Yeti in the London Underground. The impact is massive — here is where the Brigadier gets introduced (in fact, he's the prime suspect for being the Great Intelligence's vessel for most of the episode, something that would not have been done had they known he would be a regular), here is the start of the UNIT arc and here is the start of the "Yeti on the loo in Tooting Bec"-style horror that would form the Pertwee era of the show.
  • The first episode of Season 6, Episode 1 of "The Dominators", introduces us to Cully, an ageing Manchild from an alien species with two hearts, whose disgruntlement with his people makes him crave adventure and go travelling in his ship with a bunch of awkward teenagers. He lands and his entire crew gets murdered. This is an innocuous opening for a filler story at the time, but takes on a new meaning when you compare it to the last episode of Season 6, Episode 10 of "The War Games", in which the Doctor is confirmed to be a Time Lord on the run from his boring civilisation and his crew get sent back to where they were from by the other Time Lords (including the implicit death of Jamie).
  • "The Brain of Morbius" was intended as a Filler Bottle Episode, but several of the Doctor's throwaway lines in the story imply that the Time Lords aren't as godlike and advanced as they had previously been portrayed. This could easily be brushed off by the fact that the Doctor hates the Time Lords and (in that incarnation at least) has an unreliable grasp on reality, but Robert Holmes picked up on it and used it as Foreshadowing for his Wham Episode, "The Deadly Assassin", which revealed the Time Lords were a bunch of stagnant old politicians with Chronic Backstabbing Disorder. It also hints at the Doctor having regenerations predating the first seen onscreen, which wouldn't get a payoff until much, much later.
  • "Silver Nemesis" had Cybermen vs Neo-Nazis, but it set up the "Wolves of Fenric" arc with Ace and the Doctor as Chess Master motif which concluded in rather sinister style in "The Curse of Fenric".
  • "The Unquiet Dead", which introduces the Rift in Cardiff. Without that rift, the events of "Boom Town", the show's first, third and fourth series' finales and "The End of Time" would not have taken place... nor any of Torchwood.
  • "The Long Game" sets up a lot of later events — including the Ninth Doctor's regeneration — as the Doctor's actions lead to "Bad Wolf". Meaning of course that it also has perhaps the most relevant title of the entire show.
  • "The Christmas Invasion" appears to be nothing but a Christmas Episode to establish the newly regenerated Tenth Doctor, but it actually set up many events for the next seasons. There's the first appearance of the Torchwood Institute, the Santa robots come back during Donna's first appearance, the Doctor deposing Harriet Jones, Prime Minister^note Yes, we know who she is ultimately results in the Master taking her place and last but not least, the Doctor's severed hand is later retrieved by Jack Harkness and become important to both this series and the spinoff Torchwood.
  • The ending of "The Shakespeare Code" includes William Shakespeare using words from Harry Potter to stop the villains. The last episode in the season, "Last of the Time Lords", took that concept and ran with it. The relationship between the Tenth Doctor and Elizabeth I is later explored in the 50th anniversary special.
  • In series 3 of the new series, "The Lazarus Experiment" sets up both Martha's family's betrayal to Harold Saxon/The Master, and the aging device, which is used against the Doctor in the season finale.
  • Similarly, "Human Nature" and "The Family of Blood" appears to be an updated retelling of a tie-in novel, leading to a unique circumstance where fans familiar with the spinoff media were actually less likely to realize these episodes were this trope, which comes off as exceptional filler otherwise. In fact, they set up the Master's return.
  • "The Fires of Pompeii" initially appears to be a standard Monster of the Week/Historical Period of the Week episode, but even aside from the standard Casting Gags and foreshadowing for the rest of the series, the events of this episode not only foreshadow the birth of The Time Lord Victorious, and via Word of God changed the timeline, they directly influence the Twelfth Doctor's choice of appearance 6 Real Life years later (about 1200 In-Universe), which has massive ramifications for the Twelfth Doctor.
  • "The Lodger" seems like a filler episode (albeit a fun one), but we later learn that the black TARDIS belongs to the Silence, the Big Bad of the next season. Craig returns that series for a single episode, where it turns out he's the source of the TARDIS-blue envelopes from the beginning of the season.
  • "Under the Lake"/"Before the Flood" is a Base Under Siege story that seems to have the least bearing on the "Who/what is the Hybrid?" Story Arc of Series 9, especially with the next episodes introducing the season's key recurring character, but "Before the Flood" ends up heavily foreshadowing the events of the Season Finale "Hell Bent", in which the Doctor is so desperate to save Clara from her fixed-point death that he effectively becomes the villain he defeats here and threatens the fabric of space and time, something he almost did in this episode.
  • "The Ghost Monument", the second episode of Story Arc-less Series 11, is a relatively average story about the Doctor and her companions retrieving the TARDIS after it had been separated from the Doctor earlier. Come Series 12, however, it turns out to contain the first reference to the "Timeless Child", which is connected to the Series 12 arc, part of a lie embedded into Time Lord history that is so terrible it drove the Master even crazier than he already was and led him to raze Gallifrey. A throwaway line in that episode, where the villains "see deeper though, further back" gains more credence in the finale, where the Doctor finds out she is the titular Timeless Child, and has many more regenerations than she remembers.
• Farscape:
  • "A Bug's Life" has a story about Peacekeepers and a virus capable of possessing people, but the repercussions of that episode would echo throughout the series and beyond.
  • "Beware of Dog" had a fairly ridiculous main plot, with a B plot of Crichton going crazy and imagining Scorpius around every corner — but it's a brilliant setup of the entire plotline for the rest of the season, one that would continue throughout much of the series.
  • The very first time Crichton hallucinated Scorpius was in "Crackers Don't Matter", a nutty, off-the-wall episode where everyone's going crazy and fighting over crackers.
  • "A Human Reaction", a well done though not especially memorable episode - until it's revealed a few episodes later that the major plot point of the entire series was set up during its events.
  • "Won't Get Fooled Again" seems like just another one of the series' frequent visits to Bizarroworld, but the ending reveals the existence of the neural chip in Crichton's head and its accompanying mental clone of Scorpius, both of which are crucial to the Myth Arc.
  • "Eat Me" is just another Monster of the Week episode, and just another episode where Crichton gets split into duplicates (yes, it happened more than once). Then at the end it turns out that the duplication of Crichton was permanent. Cue most of the rest of the season being split between two groups of characters on separate ships, each with its own Crichton. And both Crichtons are explicitly just as "real" as the other. Since it's not a matter of one being "the original" and the other being "the copy" there's no way for the audience to peg one Crichton as an Expendable Clone; both will be equally in danger going forward rather than one being an obviously-disposable copy.
• Fringe's Bizarro Episode, "Brown Betty" (2x19) at first appears to be funny Breather Episode after some important revelations in the previous four episodes. Walter tells Olivia's niece Ella a drug-addled musical noir-style detective story using all the regular cast members... then gives the story an incredibly dark and bitter ending about how only one man can have a mechanical heart and one must die without it. The ending reflects Walter's guilt about stealing Peter and irrevocably damaging the alternate universe and how he feels the only good he's ever accomplished has come at the price of destroying children's lives (i.e., the cortexiphan trials). It reflects the major theme of the next season, that only one universe can survive; one must be destroyed, leading to the Bad Future glimpsed in the Season 3 finale, "The Day We Died". However, Ella rejects Walter's unhappy ending and creates an ending where the heart can be shared, symbolizing Peter realizing after seeing the Bad Future there is another option: he can bridge the two universes, which will heal them both. Peter even does this with the aid of a grown-up version of Ella Dunham, bringing it full circle back to "Brown Betty".
• In the second season of GARO called Makai Senki, there is a flashback episode, in which the childhood of the main character Kouga is seen. The episode seems rather unimportant, until the final episode reveals Kouga knew the Big Bad as a child, who made Kouga promise to kill him if he ever turns evil.
• Gotham's episode "The Blind Fortune Teller" appears simply to be an episode set at a circus featuring Shameless's Cameron Monaghan. Whose character then displays both a Slasher Smile and Evil Laugh, behavior very familiar to Batman fans. He doesn't actually turn out to be the Joker, but he plays a key role in corrupting the true Joker...who also happens to be his identical twin brother.
• How I Met Your Mother:
  • At first glance the "Showdown" episode seems like pure filler with Marshall and Lily preparing for their wedding and Barney going on The Price is Right. However, we learn two episodes later that Ted and Robin broke up at this time. It also sets up Barney's story arc of searching for his father that dominates most of season 6.
  • One episode features a jokey subplot in which Marshall is unable to have sexual fantasies about women other than Lily without first imaging an intricate scenario in which Lily dies of an unspecified disease and gives him her blessing to move on once she is dead. The widely-reviled ending of the show featured something similar, with the Mother dying of an unknown illness and Ted's children enthusiastically giving him the blessing to go after Aunt Robin years after the fact. Given that this ending was filmed between the first and second seasons, it's highly likely that the Marshall-Lily plot was completely intentional foreshadowing.
• Jeremiah: "And the Ground, Sown with Salt" is a fairly self-contained (albeit bloody and high-stakes) episode. However, "Tripwire" reveals that the Valhalla Sector detected the explosion of Michael's arsenal of military missiles in the climax of the episode, and were frightened and confused enough by what happened to delay their advance west by about a month, buying the heroes valuable time.
• The first half of Kirby Buckets' third season mainly focused on the cast of the show jumping through a wormhole to explore parallel universes featuring alternate versions of the show's characters. However, smack in the middle of that is what appears to be a Standalone Episode called "Commander Kirbo", an Affectionate Parody of Star Wars and Star Trek featuring, what else, sci-fi versions of Kirby Buckets characters. There is no interaction at all with the main Kirby Buckets universe, and it seems like it was just an irrelevant side plot. But three episodes later, and the characters from that dimension make their way into the main universe, and that universe's version of Principal Mitchell, first introduced in "Commander Kirbo", is the main antagonist of the season.
• Law & Order: Special Victims Unit:
  • The Season 15 episode "Wednesday's Child" has the squad finding a missing boy who was given away by his stressed out foster mother to an adoption agency who unknowingly gave him to parents who are child pornography producers. When they raid a hotel room the couple was using, they find three young girls along with an infant boy... a boy who ultimately becomes Olivia's adopted son.
• Lost had a lot of these.
  • Season 1's "House of the Rising Sun" appeared to be a standalone episode mostly intended to fill in the back story of Jin and Sun at first. Its B-plot included the discovery of two skeletons that weren't even mentioned after that point until season 6, but which turned out to be major figures in the island's history.
  • Sometimes the writers themselves didn't realize how important an episode would be until later, as was the case with Season 2's "One of Them", which introduced Henry Gale a.k.a Ben Linus, originally intended as a recurring character who would die after a few episodes, but who went on to become the Big Bad for the next season and a half, and who remained crucial to the show's mythology even after completing a Heel–Face Turn later on.
  • Season 3's "Tricia Tanaka Is Dead" is mostly a light-hearted comedy episode about Hurley, Sawyer and Jin fixing an old van Hurley finds in the woods, but the van turns out to be an important Chekhov's Gun in the season finale and the skeleton of "Roger Workman" foreshadows a major flashback storyline.
  • Season 6's "Everybody Loves Hugo". Although at first glance the episode is mostly setting up the pieces for the more dramatic twists to come, it features the Surprisingly Sudden Death of Ilana, many hints to the true nature of the Flash-sideways, and demonstrates Hurley's growing leadership qualities that ultimately lead him to become the Island's protector at the end of the series. It also features Jack vocalizing the realization that he can't take charge of every situation anymore, instead putting his faith in Hurley's judgment, which is repeated in the Grand Finale when he passes off his role of Island protector to Hurley, claiming that he's the best person for the job.
• Mad Men
  • The third season episode "My Old Kentucky Home." On its face, the Four Lines, All Waiting story serves as a series of character vignettes bound by the "work disguised as fun" theme. However, this episode introduces us characters that become prominent in later episodes (Connie Hilton, Henry Francis); and story arcs that carry through the next couple of seasons (Peggy's introduction to the counterculture, Joan realizing that marrying her doctor is not going to give her the life she thought she wanted, Betty looking for a way out of her marriage, among others).
  • The first season episode "Shoot" seems at first glance to be a character study of Betty Draper, exploring her past as a sophisticated model and what she gave up to be Don's wife. However, it introduced or foreshadowed several major elements of the show, including McCann Erickson's looming presence and desire to acquire Don, the Coca-Cola account, Don's marriage to "European, more Audrey Hepburn style" Megan, and Betty's death from lung cancer.
• The Mandalorian has "Chapter 6: The Prisoner" which, by the end of Season 1, was the only episode to not have any connection to the show's continuity. However, once Season 2 came around, a major character from "The Prisoner" reappeared to help rescue Grogu near the end of the season, gaining his own character arc and being the first human in the show to see the titular Mandalorian take off his helmet.
• Merlin had three:
  • In the first series "The Gates of Avalon" was a fairly basic Monster of the Week story, in which Arthur is targeted by two murderous Sidhe, but it also introduces the fact that Morgana is a seer which marks out her entire Character Arc from then on.
  • Series 2 has "The Lady of The Lake" introduce Freya, Merlin's love interest who dies at the end of the episode, but becomes The Lady of The Lake and helps Merlin retrieve Excalibur in the series 3 finale.
  • The third series had "Queen of Hearts", which seemed a one-off filler which once more returned to status quo by the end of the episode, but it also introduced the character of "Dragoon", Merlin's old-man disguise which he puts to even greater effect in series four.
  • Midsomer Murders: "The Sword of Guillaume" introduces DCI John Barnaby, Tom's younger cousin who replaces him at Causton CID in the next series.
• Monk: Season 4's Christmas Episode "Mr. Monk and the Secret Santa" is a standard case of the week, but has a scene that reveals that Monk is still keeping the last gift Trudy left him wrapped up. It's set up as yet another moment showcasing Monk's undying love for her. Four years later however the Grand Finale reveals the gift contains all the evidence to find her murderer.
• The Murdoch Mysteries Musical Episode is the last place you'd expect a major plot thread to be wrapped up, especially as most of it takes place inside Murdoch's mind, but the killer of the week turens out to be Ralph Fellowes, resulting in Murdoch both learning that he's still alive and finally arresting him.
• NCIS: "One Man's Trash" was a general episode involving a cold case and antique dealers. The episode also introduces the audience to Kasie Hines, the next forensic scientist of Team Gibbs and Abby Sciuto's successor, who is initially presented in the manner one would expect to see out of a one-shot or as a recurring character in this series.
• The NUMB3RS 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 we learn that that case was just the tip of the iceberg. Not only that, but 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.
• Power Rangers
  • Mighty Morphin' Power Rangers season 3's "Master Vile and the Metallic Armor" introduces the Zeo Crystal which not only serves to reverse the time shift in the Alien Rangers arc, but also its later attempted theft causes the Command Center's bombing and later serves as the basis of the next season's powers.
  • And then the premiere two-parter of Zeo mentions its Big Bad's former ties to the "United Alliance of Evil", which is later prophesied in the Millennium Message of Power Rangers Turbo, then abducts mentor Zordon and plays a big role in the Zordon Era's Grand Finale Power Rangers in Space.
  • Power Rangers Operation Overdrive's "One Fine Day" was a lighthearted episode featuring the Rangers on a camping trip which gets interrupted when their enemies erect a forcefield to search for part of the season's MacGuffin. A alien-powered human chain used as an attempt to pass through the forcefield is a major clue that the Red Ranger isn't human when it breaks, foreshadowing his Robotic Reveal character arc a few episodes later and his death-seeking Heroic Sacrifice in the finale.
  • Power Rangers RPM's "Tenaya 7" not only properly introduces the titular cyborg villainess but also before she blows her cover, a throwaway line about a metal detector getting "false positives" gains new meaning when in the two-part finale Venjix activates the sleeper drones among half of Corinth's populace including the officer who says said line.
• The Pushing Daisies episode "Circus Circus". No other episode sets up as many of the major arcs and themes in the second season: the corrosive effect of secrets; something new beginning as necessarily implying something else ending; stasis as the opposite of life/death/rebirth; the impossibility of simply picking up a relationship where it was left off; one's persona or public self versus one's True Self; a parent's inability to recognize his or her child.
• In the season 2 Roseanne episode "Happy Birthday", Dan sets up a writing room for Roseanne in the basement for her birthday, but she gets writer's block. Seven years later in the (first) series finale, the entire series is revealed to have been a book that Roseanne had written, complete with a return to her writing room in the basement as she reflects on her "real life" being different from the events of the "book".
• A season 2 episode of Sliders introduces the Kromaggs as mere monsters of the week but they become the main antagonists in the last two seasons.
• Stargate-verse:
  • Stargate SG-1: The season 8 episode "Citizen Joe" is a comedy Clip Show involving a man named Joe getting mental flashes of O'Neill's life thanks to their minds being linked by a pair of Ancient communication stones. In season 9 the communication stones come back as an important part of the story introducing the series' new main antagonists. The communication stones were later integral to the spinoff series Stargate Universe, being frequently used to allow communication across intergalactic distances.
  • Stargate Atlantis: In the first season, they encounter a planet that had been developing a drug that would make them immune to the Wraith feeding on them, but also has a 50% chance of killing the person injected. It seems like a one-off story, until the middle of season 4 when their enemy, a Wraith-turned-human-turned-hybrid gets hold of the drug and begins to spread it across the galaxy. It plays an important role in several episodes from then to the end of the series.
• Star Trek: The Original Series:
  • "Balance of Terror" and "Errand of Mercy" introduce the Romulans and Klingons, each of whom goes from Villain of the Week to major galactic power throughout the rest of the franchise.
  • "Mirror, Mirror" introduces the "Mirror Universe," which is revisited in three subsequent series.
  • The episode "Space Seed" seems at first like another example of episodic 60's-era TV—a bad guy named Khan tries to take over the Enterprise, Kirk outwits him and exiles him and his followers to an uninhabited planet, life goes on. Then Khan returns, and the ensuing events greatly influence the rest of the TOS-era movies and set up some plot points for the TNG-era series, Star Trek: Enterprise, and the reboot movies.
• Star Trek: The Next Generation:
  • "11001001" and, to a greater degree, "Elementary, Dear Data", introduce the idea of self-aware holographic programs with Minuet and Professor Moriarty, respectively, which would pave the way for other such characters like the Doctor on Star Trek: Voyager and Vic Fontaine on Star Trek: Deep Space Nine.
  • "The Neutral Zone" has two plots: the A plot is a fish-out-of-water story about twentieth-century Earth humans running amok on the Enterprise; occasionally we touch on how outposts along the Romulan Neutral Zone have been disappearing. This secondary plot is the first time in the franchise that the Borg's influence was hinted at, and similar disappearances would be discussed in their first appearance ("Q Who") and the landmark Borg two-parter "The Best of Both Worlds".
  • "The Measure of a Man" was a one off courtroom episode that focused on whether or not Data is sentient life. Turns out the philosophical implication of this episode was so far reaching that it became the primary plot of the entire first season of Star Trek: Picard. Losing this case caused Bruce Maddox to create more androids similar to Data. An attempt on the life of one of these androids kicks off the plot of Picard.
  • "Samaritan Snare" introduces the Pakleds, a species of idiots whose only edge is being just smart enough to perform a Wounded Gazelle Gambit in order to steal technology. The Pakleds return in the first-season finale of Star Trek: Lower Decks, having grown strong enough to steal Federation technology by force, and harass the Federation continually for the entire second season. The same episode would also establish the cause of Picard's artificial heart which would go on to be relevant to several stories, especially "Tapestry".
  • "Sins of the Father" is the first Trek episode to actually feature Klingon society, as Worf tries to clear his deceased father's name when he is blamed for helping the Romulans attack Khitomer, despite dying from the attacks. The episode shows that the 24th century Klingon government is extremely corrupt, as it's discovered that Duras' father was the real traitor, but the Klingon High Council goes along with it to prevent a civil war, which will have repercussions lasting all the way through Star Trek: Deep Space Nine, getting rectified by Worf, fittingly enough.
  • "The Wounded". By itself it seems like another diplomatic problem-solving episode. But it is an A Day in the Limelight episode for recurring character Miles O'Brien which sees the introduction of the Cardassians, as well as inserting a Retcon changing the previously-asserted general peace in which the Federation was said to have existed for decades and replacing it with a Great Offscreen War. This would serve as the starting point for O'Brien's promotion to main character on Star Trek: Deep Space Nine, as well as the emergence of the Maquis and the Dominion War over on DS9 — which in turn serves as the catalyst for Star Trek: Voyager. Also, Wesley Crusher's departure in "Journey's End" and the defection of Ro Laren during TNG's penultimate episode stem from this episode.
  • Ro's debut episode "Ensign Ro" also introduced the Bajorans, who would take center stage on Deep Space Nine.
  • Although made to promote Star Trek VI: The Undiscovered Country, the two-part episode "Unification" also provides Spock Prime's backstory in the reboot films, as we see that Spock was still living on Romulus as an ambassador between the Vulcan and Romulan peoples before Romulus was destroyed by a supernova. Nero, the Romulan Big Bad of the 2009 film, is led to think that Spock Prime betrayed his world, and his Roaring Rampage of Revenge radically alters history in the 23rd century. This, in turn, also provides the backstory of Captain Picard on Star Trek: Picard, which showed that Picard was also trying to save the Romulans and was so disgusted by the Federation's indifference to their fate (something Nero also pointed out) that he resigned from Starfleet.
  • "I, Borg" is the first episode in the franchise which humanizes the Borg (or more precisely, the drones who have been severed from the Collective). Hugh's introduction would eventually to lead to the characters of Seven of Nine and Icheb on Star Trek: Voyager. Hugh, Seven of Nine and Icheb would later guest star in Star Trek: Picard where one of the major themes of the show is the galaxy-wide Fantastic Racism against xBs. In Hugh's own words, "People either see us as property to be exploited, or as a hazard to be warehoused," but as Picard himself would gradually acknowledge, "They're victims. Not monsters."
  • The two-part episode "Descent" is the first episode to reveal the existence of the Borg's transwarp corridor network, as well as the fact that the Collective is based in the Delta Quadrant. Both of these facts will have major importance in Star Trek: Voyager.
  • Two simple episodes, "The First Duty" and "Lower Decks", while they tell the start of Wesley Crusher's fall from being the Enterprise's golden child and the redemption of one of those in the mess, would play a much greater role in Star Trek: Lower Decks, forming the backstory of Beckett Mariner and why she is who she is.
• Star Trek: Deep Space Nine:
  • An early Ferengi comedy episode "Rules of Acquisition" shows Quark haplessly navigating a complicated relationship while he pursues business opportunities in the Gamma Quadrant. In the process, he's told that he can't do business there without dealing with a major power known as "The Dominion". The conflict and eventual war against the Dominion became the Myth Arc of the show, and having it first appear in a comedic Ferengi episode was intentional.
  • Also from Season 5, "The Assignment" is pretty much a standard "O'Brien Must Suffer" episode, as a malevolent alien called a Pah Wraith possesses his wife Keiko and threatens to kill her and their daughter Molly unless O'Brien agrees to sabotage the station. The Pah Wraiths would become major villains in Deep Space Nine's final season.
• Supernatural
  • The early episode "Phantom Traveler" which appears to be a straight Monster of the Week episode with the brothers having to exorcise a demon who causes planes to crash For the Evulz. Not only do we learn later in the season that the one who killed the boys' mother and Sam's girlfriend is also a demon but demons become the major threat for the next few seasons with the rise in demonic possessions being a major plot point.
  • When Adam is first revealed as a third Winchester brother who was kept from Sam and Dean, he doesn't appear to have any relation to the main storyline at all, and the show even lampshades how out of nowhere it seems by naming the episode "Jump the Shark". However, Adam ends up being extremely important to the resolution of season 5, particularly for the finale.
• The Olympic special of Superstore seems like a fun little episode between seasons that also has a nebulous continuity placement in the series - but it's also the first mention of Matheo being undocumented, an element that would hang over most of his stories and impact the rest of the cast in major ways as the series went on.

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