* ActorShipping:
** It's called Stanathan. With many, many youtube videos.
* {{Anvilicious}}:
** Beckett on deficit spending, in the episode "Close Encounters of the Murderous Kind". Lampshaded, however, in that Castle, taken aback by Beckett's in-depth and forthright discussion of her views on this, has a classic "where the hell did ''that'' come from?!" moment.
** "Suicide Squeeze" hammers the 'Castro's Cuba is terrible' message home a bit too hard.
** "Countdown" takes this to a bit of an extreme level, where somehow [[spoiler:the fact that a bomb will detonate somewhere in NYC in the next twelve hours or so]] doesn't keep people from sitting around, waxing philosophic about all the different aspects of terrorism.
*** When ''else'' would you do it, exactly?
*** After The Event. ([[SarcasmMode Not the event referenced in the spoiler text]], but TheEvent. With lots of beer.)
*** The event in question would likely kill them. People tend to get philosophic when they're about to die.
** In "To Live And Die In L.A", the ending of the letter Royce sends Beckett, spelling out the fact that she has feelings for Castle she's denying, is a bit on-the-nose. Then again, this ''is'' Beckett we're dealing with here.
** Beckett talks deficit spending ''again'' in "Linchpin."
** Subverted in "Till Death Us Do Part" with Beckett's comment about the importance of keeping secrets in a relationship, as it's so clearly contradicted by [[spoiler:Ryan and Jenny's complete honesty about who Jenny's slept with]] as well as the secrets on both sides that are getting in the way of her having a relationship with Castle.
* AssPull: [[spoiler:Sophia's being the mole/Russian sleeper agent]] in "Linchpin".
* BrokenBase: Fandom's starting to show signs of this - those who dislike season four vs those who just enjoy the show for escapist fantasy.
** '''Season five'''. Castle and Beckett are now together, and some fans are annoyed with the way it's being treated - it's been compared to high school shenanigans. The finale, where [[spoiler: Castle proposes to Beckett,]] has caused an even larger divide.
** Another base is over Alexis, with those who think she's being a spoiled brat over her divisions with Castle (particularly with Pi) versus people who think she's acting like a perfectly normal daughter rebelling against her playboy father.
* CrazyAwesome: Castle's MO. [[TheMentalist Remind you of anyone?]]
* CriticalResearchFailure: Usually known for aversions, sometimes to pleased reactions from the subcultures they touch on, but there are misses.
** Season 2 episode 5, "When the Bough Breaks" and Czech Republic, its language, and its sweets.
** Season 4 episode "The Limey" featured an English police detective (played by Australian actor Brett Tucker pulling a deeply unconvincing FakeBrit accent) who was introduced as being from 'Scotland Yard'; his ID card said in big letters 'SCOTLAND YARD' and featured an elaborate multi-coloured crest incorporating, among various heraldic elements, a fleur-de-lys, which is normally associated with either France or Quebec. 'Scotland Yard' is not the name of any British police organisation but the ''nickname'' for London's Metropolitan Police Service, which has an entirely different logo (featuring a lion, a unicorn and a portcullis, among other things, but not a fleur-de-lys), and Met Police ID cards generally have the words 'Metropolitan Police' on them somewhere. To viewers in the UK, it was a bit like somebody being introduced as a Wall Street lawyer and then producing a business card giving the name of the firm as 'Wall Street'.
** Season 5 episode "Scared to Death" claims that the victims were 'scared to death', with no marks on their bodies. At the end they are found to have been killed by a modified taser delivering a shock big enough to cause an instant heart attack. Normal taser's already leave very noticeable burns when used, a police Medical Examiner would most certainly recognize them, and a higher yield one would likely leave a significantly more pronounced burn when used.
* DieForOurShip:
** Detective Demming upped the ante by [[spoiler: kissing Beckett in "Overkill",]] thus securing his status as arch nemesis of all Castle/Beckett shippers. [[Series/TheColbertReport "DEMMIIIIIIIIIIING!" * shakes fist* ]]
** As of the end of Season Two [[spoiler: Beckett broke up with Demming... just in time for Castle and his ex-wife Gina to start hooking up again. Gina's got her work cut out for her, stepping into Demming's shoes.]]
** Towards the end of "Punked," Beckett appears with a new beau named Josh. The fan hate for this particular character goes UpToEleven as of "Countdown."
*** It actually came to a head in "Rise", when [[spoiler:Josh accused Castle of getting her shot. Cut to three months later, and she's broken up with ''him,'' too.]]
** Inverted to some degree with "The Limey", however, where both Castle and Beckett seem to get (presumably) temporary new LoveInterests in flight attendent Jacinda and British cop Colin... except most of the fan ire around the episodes seems to be directed primarily at Castle and Beckett themselves, mainly for ''once again'' refusing to just [[CannotSpitItOut have a sensible, adult conversation about their issues and relationship]] and instead dicking about around the subject with other people.
** It only took the promo for "The Squab and the Quail" for fans to start wishing this upon Eric Vaughn, the genius billionaire inventor whom Beckett is assigned to protect [[spoiler: and who kisses her at one point.]] After approximately two seconds of footage, he has apparently skyrocketed past even Josh as the most hated character in fandom. Considering that Josh is blamed by this same fandom for everything bad everytime (see MemeticMutation), this is saying something.
** Much like the BrokenBase above, Alexis gets some hate for this, as well, apparently because her "bratty antics" take away from "Caskett time". Also, some think she doesn't like Beckett for some reason.
* EarWorm:
** The show's theme tune deserves a mention here.
** The victim's [[spoiler: eventual-murder-solving]] last song from "Famous Last Words". And they play it ''constantly'' throughout the episode. Auuuugh.
** [[http://www.youtube.com/watch?v=VDbuOQdV5A4 Get on the Floor]], from "Lucky Stiff."
*** InUniverse, too, since Beckett is later seen trying to do an acoustic guitar version of the track.
** [[{{Pink}} The ringtone from "Nanny McDead".]]
* EnsembleDarkHorse:
** Lanie the Medical Examiner seems to be going this way. As of season two, she's been showing up more with bigger lines that aren't strictly about the case of the week. But then again, she also gets some of the best lines and could probably match wits with Castle so it's understandable. Fellow Medical Examiner Perlmutter gets some great snarks in on Castle, as well.
** Detectives Ryan and Esposito have ended up becoming quite popular with the fans to the point of almost getting as much screen time as Castle and Beckett, but the charmingly {{Adorkable}} Ryan in particular might fit this trope most -- he wasn't even supposed to be in the series initially, and was a relatively last-minute addition after test audiences didn't respond well to the detective who was initially supposed to take his place. He even has a CharacterBlog on ABC.com.
** Captain Montgomery most definitely. Whenever he shows up, one can be certain he'll do or say something awesome. [[spoiler:His death at the end of "Knockout" was no different and you can bet the [[TearJerker tears]] flowed like rain.]]
** West Side Wally in season four. He first showed up in ''"The Blue Butterfly,"'' but made a reappearance in ''"47 Seconds."'' Lampshaded by Esposito.
--> '''Esposito''' West Side Wally, [[LeaningOnTheFourthWall back by popular demand]].
* FridgeBrilliance: In a rare case of this trope being taken literally, this is [[LampshadeHanging lampshaded]] occasionally by Castle and Alexis. In several episodes ("A Chill Goes Through Her Veins" and "A Deadly Affair", for example), facing logical puzzles or romantic dilemmas, they open the refrigerator and hang mournfully on the door, staring inside. Castle at one point comments, "What is it about the refrigerator? Is it the cold? The light? Or some combination of the two?"
** In "Suicide Squeeze", the wife's victim thought he was having an affair with a woman that appeared in a photograph with him, who turned out to be the victim's daughter (the aforementioned 17-year-old). Given that she looked like a short adult, is it too outlandish that the wife thought the girl was her husband's lover? One of the few cases where DawsonCasting actually works!
* GrowingTheBeard: Although the series was well-received in seasons one and two, putting Castle and Beckett together in season five appears to have given the show a critical and audience appreciation shot-in-the-arm after the SeasonalRot of seasons 3 and 4 discussed below. Even the cast and crew seem just a bit more enthusiastic about the show now.
* HarsherInHindsight: Not so much harsher but [[spoiler: sadder in that after the events of "Knockout", everyone knows exactly why Montgomery is so lenient with Beckett.]]
* HilariousInHindsight:
** In the pilot, at Castle's poker game after the premiere of the final Derrick Storm novel, JamesPatterson quips, "You certainly don't see me killing off Alex Cross." A few months later, he's advertising his next Cross book by saying "Buy this book, or I'm gonna have to kill Alex Cross."
** In "Hunt" James Brolin turns up as [[spoiler:Castle's long-absent father]]. Just over a week later, he turned up on ''Series/{{Community}}'' as [[spoiler:Jeff's long-absent father]].
* HoYay: Ryan and Esposito. Oh so very much.
** In "Den of Thieves", the word 'partner' is used repeatedly in questionable context.
** Also in the same episode: "Where's Esposito? WHERE'S ESPOSITO?
** In "Lucky Stiff" [[TheIngenue Ryan]] reveals that he plays Esposito's lottery numbers, so it wouldn't be awkward if one of them won. [[ComicallyMissingThePoint Uhm]] [[DiggingYourselfDeeper yeah...]]
*** Even moreso because Esposito's numbers are the dates of his firsts - as in, his first time in combat and the first time he had sex.
** Castle to Esposito about Ryan when Ryan's girlfriend calls him yet again.
-->'''Castle''': Don't worry, he still loves you.
** Ryan and Esposito discussing the JonasBrothers
-->'''Beckett''': When I'm not here, do you guys braid each other's hair and discuss who's your favourite Jonas brother?
-->'''Esposito''': No... but it's Nick.
-->'''Ryan''': Absolutely Nick.
** Esposito throwing Ryan up against a wall in "Knockout", [[spoiler: after finding out that Captain Montgomery was involved in Johanna Beckett's murder]]. And the heads of a thousand SlashFic [[YaoiFangirl writers]] exploded...
** It gets better in "Dance With Death", when a (keep in mind, married for seven episodes) Ryan pretty much insists Esposito wear his wedding ring when interviewing suspects at a strip club... to see if strippers will flirt with him even if he's not taken. The scene is set up to look like a proposal, which isn't even mentioning the subtext that Espo gets a date because of the ring... and later, can't take it off because his finger's too big and needs Beckett's hand cream. Ryan panicked. Slashers squealed.
** The best thing about the HoYay here is that Esposito and Ryan pretty much acknowledge the fact that it's there and just roll with it.
** Between Castle and his old high school friend Damian in "The Last Nail." Teenage boy sent off to a boarding school, gets homesick, and gets comforted by an older student.
** In "Probable Cause", Esposito assures Beckett that she's not alone in worrying over Castle's situation as the prime suspect of their current murder investigation.
-->'''Esposito''': I know how you feel about the guy. I love him, too.
** In seasons 6's episode "A Murder is Forever", the victim of a week is a renown relationship therapist with a best-seller on relationships, and after having read it Ryan refers to it... but in the context of his relationship with Esposito, ''not'' his wife.
** In "Under Fire", with Ryan and Esposito trapped in a burning building and Ryan's wife going into labor, they manage to contact the crew, and Jenny asks her husband what to name the baby. His response for a boy's name is "Javier". Even Espo criticizes that choice. Luckily for both of them it's a girl.
** In the Season 4 blooper reel, Creator/AdamBaldwin grabs NathanFillion's butt. He responds by swatting his hand away and saying, "Later."
* LesYay: The killer in "The Mistress Always Spanks Twice" is the victim's female roommate, whose MotiveRant for killing is loaded with LesYay with a PsychoLesbian twist. Add in the fact that the victim once compared her to a dominatrix...
** The female plastic surgeon in "Disciple" is absolutely ''fascinated'' by Beckett's "perfect face" and takes every opportunity to invite Beckett to come in and have some work done. [[spoiler: Gets far, far creepier once it turns out it is extremely probable she was the real mastermind behind the killings and picked up all of 3XK's methods by dint of being his lover.]]
* LikeYouWouldReallyDoIt:
** At the end of "Tick, Tick, Tick" it looks like [[spoiler: the villain of the two-part episode has blown up Beckett in her apartment. Of course she wasn't.]]
** The trailer for season 3 shows the cops busting in and finding Castle over a dead body holding a gun. Clearly he did it and will be sent to jail for the rest of his life.
** "3xk" [[spoiler: has the -real- climatic scene involve a serial killer with Castle at his mercy.]] The scene cuts abruptly after the killer threatens Castle. Of course, Castle isn't killed but, at least in the killer's and Castle's mind, that may be a FateWorseThanDeath.
** "Setup" / "Countdown" has a triple-whammy:
*** Castle and Beckett encounter the remnants of a highly radioactive device removed from a storage locker.
*** Castle and Beckett are locked in a freezer.
*** Castle and Beckett find themselves face-to-face with a dirty bomb counting down to zero. Obviously, it will explode, killing them and irradiating a good chunk of downtown Manhattan and its population, and they will not be able to do anything to prevent this. And if you believe any of the above spoilers, there is an excellent bridge property in Brooklyn for sale at a very generous price...
** [[spoiler: "Knockout" ends with Beckett shot and lying in Castle's arms, during which he finally whispers that he loves her. The entire fandom is sure she's not going to die, but the repercussions of the gunshot are the real issue.]]
** "Probable Cause": It was highly unlikely that the main character of the series would be revealed to be a sadistic murderer who would be sentenced to prison six episodes in to the season. Slightly (but not much) more in-doubt, however, was the question of whether he had been cheating on Beckett with the victim.
** "Valkyrie". [[spoiler: Castle has been exposed to an aerosolised biochemical agent giving him one day left to live. Obviously, he will die in the second episode of the series, leaving Beckett without a fiance and the series without a main character.]]
** The very end of "For Better Or Worse": Yeah, sure, [[spoiler:you're gonna kill off the title character by running him off the road in a fiery conflagration. We all believe that one.]]
* MarySue: Alexis has all the makings of this - the [[PuritySue perfect daughter]] who is only grumpy when Castle's being unreasonable, shown to be a brilliant detective without any training and never does ANYTHING wrong without apologising tearfully to her dad. Go on, try to find an episode where she does anything considered remotely negative.
** As of the fourth season however, this seems to have been toned down what with her failing to get into Stanford on early admission, and having a very large meltdown over it, as well as the WordOfGod that she will be getting unreasonably resentful of Beckett during the season.
* MemeticMutation: Due to his incessant cockblocking in Season 3, [[RomanticFalseLead Josh Davidson]] has earned the reputation on Tumblr of being blamed for anything negative that happens in the fandom or the show, from the cast not winning awards to problems on the show itself. It is almost always capped with the [[http://media.tumblr.com/tumblr_lvhb8a1nlH1qfpz6o.jpg following picture.]]
** In-universe, there's Johnny Vong's commercial, which Castle and Esposito recite.
* MoralEventHorizon: You can sympathize with the motives, if not the actions, of the terrorists in "Countdown" [[spoiler: embittered soldiers who feel abandoned, betrayed and ignored by their country and their government]], but any sympathy goes out the window when they kidnap a mother and her baby (the husband and father of whom they'd already murdered), hold the baby hostage, all but threaten to kill her and [[spoiler: force the mother to drive a truck carrying a dirty bomb into the city, which will ultimately frame her as the terrorist when it explodes]].
* NarrowedItDownToTheGuyIRecognize: The show appears to take delight in [[ZigZaggedTrope zig-zagging furiously]] on this trope:
** "Inventing the Girl": Julian Sands [[spoiler:''didn't'' do it.]]
** "When the Bough Breaks": [[HomicideLifeOnTheStreet Reed]] [[{{Dollhouse}} Diamond]][[spoiler: did it.]]
** "Little Girl Lost": Francis Capra, AKA [[Series/VeronicaMars Weevil]], and Judy Reyes, AKA [[Series/{{Scrubs}} Carla Espinosa]]. [[spoiler:Capra's a red herring, but Reyes isn't.]]
** "Kill the Messenger": Gregg Henry pops up. Anyone GenreSavvy enough to know about this trope went "Oh. Oh ''[[ForegoneConclusion well]]''." [[spoiler:Subverted.]]
** [[TwinPeaks Ray]] [[Series/{{Reaper}} Wise]] in 2x15, "Suicide Squeeze". [[spoiler: Played straight.]]
** "One Man's Trash": features DB Woodside, ''[[Series/TwentyFour 24]]'''s Wayne Palmer and Series/BuffyTheVampireSlayer's Principal Wood, as well as Perrin "[[{{Entourage}} Mrs. Ari Gold]]" Reeves and Abigail "[[MadMen Miss]] [[Series/HowIMetYourMother Blah-blah]] [[MadMen Farrell]]" Spencer. [[spoiler:Subverted for the women, not so much for the guy.]]
** Played with like a kitten's ball of string [[spoiler: and averted]] in "The Mistress Always Spanks Twice". Lesse, the deceased was a post-grad who had [[GilmoreGirls Lane Kim]] and [[MySoCalledLife Brian Krakow]] vying for the same award, so it must've been one of them, right? She also went undercover as a dominatrix in an S&M club whose proprietor is [[{{Saw}} Dina Meyer]], so maybe it's her? [[spoiler:Nope: it was her roommate, who was played by a relatively unknown actress]].
** "Wrapped Up in Death", Navi Rawat (AKA Amita from {{Numb3rs}}), Erick Avari (crazy Dr. Bey from ''{{Film/The Mummy|1999}}'') and Currie Graham (from ''DesperateHousewives'', [[HeyItsThatGuy among others]]). [[spoiler:Currie Graham did it]]. [[spoiler:Currie Graham ALWAYS is the murderer, unless he's a series regular. No exceptions.]]
** "The Late Shaft" averts this by salting the suspects with enough B and C-list celebrities for a VH1 reality show. [[AmericasFunniestHomeVideos Tom]] [[DancingWithTheStars Bergeron]] played the big late-night talk show host [[spoiler:victim]]; Fred Willard played his feisty sidekick, [[Series/SabrinaTheTeenageWitch Beth Broderick]] played his first wife, Bill Bellamy played his heir apparent, Dan Cortese played the network president, Kelly Carlson played another guest [[spoiler:who hooks up with Castle]], and even [[ThirdRockFromTheSun French Stewart]] [[PlayingAgainstType played a skeevy guy who did business with Bergeron]]. [[spoiler:Fred Willard dood it.]]
** Mitch Pileggi [[HeyItsThatGuy a.k.a]] [[Series/TheXFiles A.D Walter Skinner]] turns up in "A Deadly Game" as a hardened spy / assassin. [[spoiler: Hilariously subverted; turns out he's just some hapless schmuck on a spy vacation who thinks that this is all part of the game. Once he realizes he's in "real jail", [[PlayingAgainstType he bursts into tears]].]]
** Muse Watson aka [[Series/{{NCIS}} Mike Franks]] in "Punked". [[spoiler: Didn't do it]].
** "Close Encounters of the Murderous Kind" has LyleLovett and [[Film/{{Aliens}} Bishop]]. [[spoiler: The killer was someone else.]]
** "One Life to Lose" features ''AllMyChildren'' regulars Rebecca Budig and Cameron Mathison, [[Series/DrQuinnMedicineWoman Jane Seymour]], [[Series/SexAndTheCity David Eigenberg]], [[Series/{{Psych}} Corbin Bernsen]], and [[Series/VeronicaMars Tina Majorino.]] [[spoiler:That last one did it.]]
** "Head Case" features [[{{Entourage}} Adam Davies]] [[spoiler:(suspicious but didn't do it)]], [[Film/TeenageMutantNinjaTurtles April O'Neill]] [[spoiler:(did it and then herself)]], [[Film/DieHard Richard]] "[[Film/{{Ghostbusters}} Dickless]]" [[Film/DieHard Thornburg]] [[spoiler:(a subverted CorruptCorporateExecutive)]], and [[Film/IronMan Yinsen]] [[spoiler:(stole the victim's head, but [[ItMakesSenseInContext with justifiable reason]])]].
** In "Demons": Has [[spoiler: Frederic Lehne]] ever played a good guy?
** In "Blue Butterfly": Creator/MarkPellegrino, who has played {{Satan}} of all villains, appears as Tom Dempsey, a mobster in 40s [[spoiler: and also his grandson Tom Dempsey III]]. Turns out that [[spoiler: he was innocent of the murders in ''both'' cases]]. Infact, [[spoiler: the grandson was a NiceGuy]].
** "Dreamworld" guest-stars Warren Christie -- Cameron Hicks from ''Series/{{Alphas}}''. [[spoiler:Guess who's the killer]].
** [[Series/TwentyFour Annie Wersching]] and [[{{Series/Lost}} William Mapother]] show up in "Disciple". [[spoiler:Mapother's character cops to the killing, but it's Wersching's character who is the titular disciple... to 3XK.]]
* NightmareFuel: Undead Again is horrifying with the Zombies.
* OneSceneWonder: Several witnesses, suspects, and other minor characters have their moments.
** The old guy in "Nanny [=McDead=]" who -- when Castle and Beckett conclude that he couldn't have been the one that the victim wanted to have sex with -- shouts after them, "Seventy-seven ain't beyond the realm of possibility, you know!"
** Introduced in "Punked", Ashley, Alexis' boyfriend, is accidentally [[TwerpSweating Twerp Sweated]] by Castle in what was, for a while, his only on-screen appearance.
** Vulcan Simmons, a GenreSavvy SmugSnake suspect in "Knockdown." He doesn't show up again until season 6, when he's shown to be running a drug operation to fund Senator Bracken's campaign for President. Then he appears in "Veritas", as part of an elaborate frame job meant to take Beckett out once and for all.
** In "The Final Nail", a carpenter with an Eastern European accent that [[GotMeDoingIt gets Beckett to accidentally mimic his accent]].
** Westside Wally, a homeless guy who insists on being called "Westside", appearing in "The Blue Butterfly". He returns in the episode "47 Seconds", reintroduced by Esposito:
--> '''Esposito:''' Westside Wally. Back by popular demand.
** Dr. Barker, the somewhat nutty dog doctor-slash-dog whisperer in "An Embarrassment of Bitches". It doesn't hurt that she's played by the always utterly charming Creator/NanaVisitor.
** Gene Simmons was hilariously laconic and jaded: "Yeah, yeah, from Kiss. Yeah, yeah, with the tongue."
* RescuedFromTheScrappyHeap: Gates seems to have shaken off the hatred piled upon her when she arrived, especially now that she's been revealed to have her own quirks and HiddenDepths.
* RomanticPlotTumor: Whether you like it or not, the Castle[=/=]Beckett relationship is and always has been a central driving engine of the show so isn't one of these. The 'significant others' plot arcs of the latter part of season two and season three, however, are generally disliked by the fans because they break up Castle and Beckett (the chemistry between the two generally being considered one of the show's great strengths) and shove them with other people in a predictable and angsty way that seems to have little point other than to act as a 'roadblock' that kills time and prevents them from getting together.
* TheScrappy: Pi, Alexis's boyfriend in Season 6, who is basically what you get when you cross a CloudCuckooLander and a [[GranolaGirl Granola Guy]] together. Few fans have any kind things to say about him.
* SeasonalRot: The third and particularly fourth seasons have come in for some criticism from various quarters, with probably the most frequent criticism being that the Castle[=/=]Beckett relationship keeps getting bogged down in various angsty misunderstandings and 'roadblocks' designed to artificially stretch out the 'will they, won't they' angle (despite the fact that it's frequently made very clear that they ultimately will), in comparison to the more fresh and light-hearted approach taken in seasons one and two. It's fair to say that the ending of "Always" went some way towards mollifying many of these critics, however, and WordOfGod indicates that the fifth season will see a return to the more light-hearted approach taken by the first two seasons.
* ShippingBedDeath: {{Averted}}. The resolution of Castle and Beckett's {{UST}} only brought on a fresh new source of tension and humor, specifically how they keep their office romance a secret.
* SpecialEffectFailure: In "Hunt", the scene in which Castle talks on a payphone in Paris has him standing in front of a very obvious and fuzzy green screen. Turns a serious scene into {{Narm}}.
* TakeThatScrappy: Alexis's entire rant about Pi in episode 13 of season 6 more or less sums up precisely why the viewers don't like this guy. A few episodes later, she reveals she broke up with him off-screen.
* TooCoolToLive: [[spoiler:Roy Montgomery]].
* TooSoon: The episode "Still", which features Beckett being caught on top of a pressure-sensitive bomb, was pushed back one week following the Boston marathon bombings (and Boston ABC affiliate WCVB-TV elected not to air it even after it was pushed back). TNT failed to get a repeat of "47 Seconds" (another bomb plot) out of its Wednesday rotation and later apologized.
* TheWoobie:
** Castle became this in the episode "Wrapped Up in Death" after supposedly being cursed by a Mayan Mummy. The fact that Beckett, Ryan, and Esposito kept playing pranks on him to make him believe in the curse only made it worse.
** His face when he sees [[spoiler: Beckett kiss Deming]] at the end of "Overkill" is absolutely heartwrenching.
** Beckett at the end of "A Deadly Game" [[spoiler: She begins to work up the courage to tell Castle how she feels about him, something which does not come easy for her, but just before she can his ex-wife Gina makes an appearance. The look on Beckett's face as they leave together speaks volumes.]]
** For a while, Castle is this during the Season 3 opener "A Deadly Affair" because the entire precinct is giving him the cold shoulder for not returning sooner or calling at all during his absence. Sure, he deserves some of it, but you do feel a little bad for the guy after a while.
** Cesar Calderon from "Anatomy of Murder" is an odd case. [[spoiler: Yes, he's was a ruthless drug lord responsible for a lot of bad things... but he's also completely innocent in the murder and his horrified revelation of the killer is pretty darn heartbreaking. In fact, he was in love with the victim and it's implied he was going to marry her. The culprit? His own brother who killed her and tried to dispose of the body in the same way as in their drug lord days (ie no body at all so she basically just disappears). Even worse, there was no reason for her to be killed in the first place because the reason the brother thought was basically incorrect. Had the brother done the first thing Cesar says (talk to him and let them confront her about it), none of it would have happened at all.]]
** Castle in "47 Seconds". [[spoiler:He is about to tell Beckett for real that he loves her, but he gets interrupted by Esposito before he can do it, so he decides to do it later. However, when Beckett is interrogating a suspect, he goes to the adjoining room to hear the interrogation, and discovers that Beckett actually remembers everything that happened after being shot. He is, naturally, left broken at the fact that Beckett decided to deceive him, and the rest of the episode, when he is not helping with the case, he acts passive-aggresively towards Beckett.]]
*** Beckett might also count here as well, to some degree at least; [[spoiler: despite keeping her secret, she was also planning on taking things to the next level and, unaware that Castle has found out her secret, is understandably bewildered and hurt by his sudden u-turn in attitude.]]
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