The Castle-Beckett relationship is the flirty/friendship relationship between Richard "Rick" Castle and Katherine "Kate" Beckett. Their couple name is most commonly referred to by shippers as Caskett.
Beckett's initial relationship with Castle was strained because she viewed him as immature and reckless. She suspected (correctly) that Castle was using his "research" as an excuse to pursue her, and only tolerated his presence at the request of Captain Montgomery. While she came to respect the value of his unique perspective on crime, she remained frustrated with him on a personal level. This frustration reached a boiling point when Castle, against Beckett's wishes, re-opened her mother's murder case. She was angry and hurt, and requested that he ends their relationship. Only when he apologized and agreed to end the partnership did she relent and offer to let him stay ("A Death in the Family").
Castle continues to pursue Beckett, while she still fends him off. However, the flirtation is now two-way, and there are signs that she sees Castle as more than just a friend. While hotly denying it, she is clearly grief-stricken in "When the Bough Breaks" when it seems that Castle will be ending their partnership now that he's finished writing Heat Wave.
In "A Rose for Everafter", Castle reunites with an old flame. Kyra Blaine is not what Beckett would have expected: she is intelligent, serious, and caring. Beckett tells Castle, "She's real. I didn't think you'd go for real." She is also clearly jealous of Castle's feelings for her. We also see Castle from a new perspective. He was heartbroken when Kyra never spoke to him again after a "break" in their relationship, and this puts the more shallow women he's been with in a new light. Like Beckett, emotionally isolated after the loss of her mother, Castle avoids taking emotional risks by staying in superficial relationships.
The first major turning point in their relationship was in "Sucker Punch", when Castle spent $100,000 of his own money to catch the hit man who killed her mother. Castle was taken hostage when their informant turned out to be the hit man himself, and Beckett was forced to kill him to save Castle. Dick Coonan died before revealing who hired him, and Castle, blaming himself, offered to end their partnership. Beckett asks him to stay. She explains that she's "gotten used to you pulling my pigtails" and that he's made her job more fun. From then on, the banter between them becomes more affectionate and playful, and a genuine friendship develops.
In "Tick, Tick, Tick…", Beckett's jealousy is professional, not romantic, as Castle's attention focuses on Agent Shaw, her reputation as a brilliant profiler, and her high-tech equipment. Agent Shaw immediately sees the chemistry between the two and assumes that they're already sleeping together. Beckett expresses horror at the idea. Shaw later comments on Beckett's emotional isolation, and tells her that Castle genuinely cares about her. Beckett, clearly conflicted, tells her that the situation is complicated ("Boom!").
This does not prevent either from entering romantic entanglements with others. Castle has a fling with a movie star, not realizing that she's really gunning for a part in the movie adaptation of Heat Wave ("The Late Shaft"). Beckett then develops a romance with a handsome young detective, Tom Demming. This relationship becomes increasingly serious, and Castle's jealousy makes him increasingly hostile and competitive with Demming.
In "Food to Die For", Castle and Beckett discuss their victim, killer and the girl caught in between. Castle says that the girl should have gone with the one she obviously truly loved, and Beckett argues that she saw the logic in staying with the one that seemed responsible and more dependable at that time, as opposed to the one with a history as a playboy that makes you feel good for a while, but has a risk of just letting you down eventually. Castle replies that she should have just followed what the heart wanted since things would have turned out well for them as the former playboy turned out to have been planning a proposal before he died. The conversation is their indirect reference to the current situation between themselves and Demming.
In "A Deadly Game", Castle makes a last attempt to win Beckett over, by inviting her along on his annual Memorial Day trip to the Hamptons. Beckett refuses, claiming she is busy, but it quickly becomes clear that she will be on a different beach—with Demming. Realizing that he's lost, and Demming has won, Castle ends the partnership on the pretext that he needs to finish his book. While he claims he will be gone for the summer, Beckett and the other detectives realize that this might be a permanent parting.
Unknown to Castle, Beckett has re-examined her feelings for him. Desperate not to lose Castle, she breaks up with Demming and approaches Castle to declare her own feelings for him. But it's too late: Castle has already planned to go to the Hamptons with another woman: Gina, his ex-wife, with whom he's re-kindled a relationship. Castle explains this, believing that he's gracefully stepping aside, but this crushes Kate, who waited too long and took an emotional risk for nothing. ("A Deadly Game")
Castle returns after the summer, but does not call Beckett or the precinct. The detectives, especially Beckett, feel snubbed, and she assumes that he didn't call because he doesn't really care about her. Castle, for his part, assumes that she's still with Demming and has procrastinated about contacting Beckett again because of his unrequited feelings and a sense that things might not be the same. They are forced together when the detectives arrive at a murder scene to find Castle standing over a dead body while holding a gun. Though he explains the victim was an acquaintance that called him for help, he is arrested for murder and interrogated by Beckett at the precinct. The questioning quickly turns to a reflection of what Beckett feels was Castle abandoning her. Stung by the snub, Beckett doesn't want Castle back, but he eventually regains her trust. ("A Deadly Affair") Things proceed much as in Season Two: Castle and Beckett are friends, and while each wants something more, outside events and their own emotional issues keep them apart. Executive Producer Andrew Marlowe refers to this as "the dance". The two enjoy witty banter and unresolved sexual tension, but without the fulfillment of actually engaging in a relationship. Eventually, she comes to refer to him as her partner, as if he were another officer, but tacitly acknowledging that the two are more than just friends.
Nevertheless, the two continue to pursue relationships with other people. Castle remains with his ex-wife Gina, though the relationship remains stormy and the two break up in "Poof! You're Dead". However, by this time, Beckett is now in a relationship with Josh ("Punked"), a philanthropic doctor, whom she remains with through the rest of the season.
In "3XK", Castle is left in a hotel room tied to a chair by a serial killer (Jerry Tyson). Beckett rushes to the room scared that Castle may have been killed. But Castle has been left knowing that Tyson is free to kill again, and forced to live with the guilt at having failed. The closing scenes of this episode clearly show their emotional connection: Beckett's terror that Castle might be dead, and then her compassion when she sees how depressed his is over his failure. The two hold hands for the first time; "the dance" continues. As always, Castle pursues a relationship with Beckett, while she continues to fend him off. However, despite her boyfriend, it's clear that she harbors secret feelings for him.
In "Nikki Heat", Beckett becomes jealous of superstar Natalie Rhodes, who is preparing to play Nikki Heat in the movie? Dressed as Beckett and imitating her mannerisms, she's the next best thing to the real thing. Beckett's jealousy at seeing Castle kissing her in the elevator is obvious... but Natalie later reports that Castle is the first man who's ever turned her down. She deconstructs their relationship for Beckett: that Castle wants her, but she's refusing to give in to feelings she clearly has for him. Beckett is shocked, but doesn't deny the truth of Rhodes's read of the situation.
In "Knockdown", Castle and Beckett finally kiss for the first time. Although this is a ploy to distract a guard and save Ryan and Esposito, there is much more to the kiss than a simple ruse. In "Setup", Beckett acknowledges that she and Josh are having problems, stemming from a sense that he's not really there for her. Later, in the same episode and the second part, "Countdown", the two are trapped in a freezer. Huddled together and slowly dying of hypothermia, the two express the depth of their commitment to one another, but do not quite admit their love. Castle wakes to find Beckett being treated by Josh, who she says she thinks she has a chance with. Later, Castle is about to admit his feelings for her, but Josh walks in, and he leaves instead, heartbroken.
Castle's jealousy isn't limited to Josh. In "The Dead Pool", she is "courted" by another writer, Castle's protege Alex Conrad. At the end of the episode, Castle admits openly to being jealous and she responds by committing to be a "one writer girl". In "To Love and Die in L.A.", the two are staying together in a hotel room, where Castle begins to make a move on Beckett. She immediately backs down and walks out terrified. In her room, she collects herself and goes back out to talk to him, but he's already gone to bed. In "Knockout", Castle must choose between his relationship with Beckett and saving her life. Montgomery and Beckett's own father urge him to talk to her, to tell her to stop pursuing the case. Castle confronts her, and the heated conversation segues to the question of exactly what their relationship really is. The argument escalates, and she throws him out, ending the partnership. Despite his role in getting Castle to speak out against the investigation in the first place, Montgomery quickly agrees to eliminating Castle. Beckett had expecting him to argue with her, and has second thoughts, but holds her ground.
What she doesn't count on is that Montgomery has been involved in the conspiracy from the beginning, but has also been protecting Beckett. He has Castle intervene to make sure that Beckett doesn't get herself killed as he sacrifices himself to save her. He is only partially successful; Hal Lockwood is dead, but another assassin shoots Beckett at Montgomery's funeral. As she lays, seemingly dying, in Castle's arms, he confesses that he loves her.
The new season opens moments after Beckett is shot and Castle has made his declaration of love for her. Beckett survives, and tells Castle that she does not remember her shooting describing it as just everything "going black". She also asks Castle to give her a few days to get things back together. Castle agrees, but days turn into months with hearing no contact from her. He doggedly pursues the case, but there are no leads and the new Captain, Victoria Gates, is hostile to Castle and throws him out. When Beckett finally contacts Castle at a book signing, clearly surprising him, he is at first bitter toward her for not contacting him and is reluctant to return. He only finally makes peace with her when she mentions that she and Josh broke up. ("Rise")
This season is about secrets as both Castle and Beckett have something big to hide. Castle's secret is that Montgomery arranged to protect Beckett's life through blackmail; Castle's role is to make sure that Beckett stays off her mother's case. He secretly pursues the case himself, in her stead. Beckett's secret is that she heard Castle professing his love, but pretended to have no memory of the event. These results in a much darker dynamic to their relationship, but they are also more open than they have been in the past to hinting at possible romance. In "Heroes and Villains", they encounter another writer/cop team, who have consummated their relationship, and Beckett's advice to her counterpart is to encourage their romance. In "Eye of the Beholder", Beckett reluctantly encourages Castle to pursue a relationship with sexy insurance investigator Serena Kaye, but apart from some sparks flying between the two, he doesn't. "Cops & Robbers" features some very meaningful looks when Beckett rescues Castle from a hostage situation at a bank, but again they do not explicitly acknowledge their feelings although they are more than clear. In "Cuffed", the two spend the entire episode handcuffed to one another; the episode ends with Castle saying that there was no one he'd rather be "hitched" to. Beckett agrees, but suggests that they "leave out the tiger next time". When Kevin Ryan marries Jenny, the episode ends with Castle and Beckett going to the wedding as a couple, and closes with the two walking down the aisle towards their seats ("Till Death Do Us Part").
In "Dial M for Mayor", Castle defends his friend the mayor accused of murder. Forced to choose, Beckett ultimately chooses her professionalism over Castle. She takes actions that she knows would eventually led to Castle being thrown out by Gates. Though the mayor's career is effectively ended, Castle remains at the precinct.
The Castle/Beckett relationship faces yet another long-lost flame in the form of Sophia Turner. Turner is, on the surface, a perfect recipe for Beckett's jealousy. She's a glamourous and highly skilled CIA agent, a former muse of Castle, the inspiration for Clara Strike from his Derrick Storm novels. She was also involved with Castle sexually. Castle won't discuss their relationship, but Sophia does. Several times, she hints to Beckett that things ended badly due to his irresponsibility and immaturity. She flat-out tells Beckett that she regrets sleeping with him that doing so killed the magic in their relationship, which she hints was just like his with Beckett. In private, she plays on Castle's feelings for her, showing warmth and affection for her ex. ("Pandora", "Linchpin") Sophia is actually Castle's worst fear: a former flame who never really loved him and was only using him and laughing. In the end, Beckett chooses not to accept Sophia's version of events and continues to believe in Castle instead.
However, even as Beckett begins to entertain the possibility of a romance with her partner, Castle's own fears begin to take center stage. In "47 Seconds", he inadvertently discovers definitive proof that Beckett did in fact hear and remember his confession of love and has been lying for seven months about it; Castle takes this as meaning that she doesn't have feelings for him and was letting him down easy by pretending she hadn't heard. Castle resolves to make their relationship purely professional. He begins a string of casual affairs, returning to his playboy past. When dashing British detective Colin Hunt teams up with Castle and Beckett, Castle ignores the rival and encourages the two to work together. Ironically, this comes right when Beckett finally confesses her feelings for Castle to Lanie. Lanie had warned that Castle wouldn't wait forever for Beckett, and now it seems she has finally chosen to act too late. ("The Limey")
Castle even finds a new detective to follow around (Ethan Slaughter), but his disregard for the law almost puts the wrong murderer in jail. Beckett comes to his aide, risking her job to protect her partner. Her therapist has helped her understand why Castle is distancing himself from her, and she realizes that he's been throwing himself into empty relationships to protect himself emotionally. ("Headhunters")
While Beckett remains surprised and hurt that Castle has suddenly begun to distance himself from her, she still has not figured out what's triggered this abrupt change. Meanwhile, Castle realizes that he can't cut his feelings away while he remains partnered with Beckett, and resolves to end the partnership. He obliquely hints at both this and his knowledge that she lied to him. She responds by telling him that she's been in therapy for her emotional distance issues, and is nearly ready to have the kind of relationships she wants to have. Castle agrees to stay with her. ("Undead Again")"Always" is in many ways a reprise of "Knockdown". A lead in the killing of Beckett's mom comes when the mysterious killer acts to cover up his crime. As the body count rises and the size of the conspiracy becomes evident, Castle confronts Beckett and insists that she abandons the case to save her own life.
This time, he finally reveals his own dirty secret; he has participated in the cover-up to protect her. When Beckett angrily demands to know why he would do that, he finally confesses his love openly to her and asks her to choose between him and the case which has defined her, but Beckett refuses to put the case behind her and says it is her life to live. Castle allows her to make her choice, but says that he refuses to watch her throw her life away and ends their partnership before leaving. Beckett fails to catch the killer (Cole Maddox) and is left literally hanging from the edge of a building. Crying out for Castle to save her, it is Ryan and Captain Gates that come to her rescue. She finally realizes that Castle is really gone for good. Beckett, facing suspension for misconduct in her handling of the case, chooses to resign instead. That night during a heavy rainstorm, she returns to an initially resistant Castle desperate to say how sorry she is. Kate explains how Maddox got away, and that she nearly died but all she could think about was him and says to Castle, "I just want you". Castle's resistance breaks down and the two begin to kiss passionately before they go to Castle's bedroom together and make love for the first time.
Season FiveEdit"After the Storm" opens with the morning right after Castle and Beckett's first big night together. Castle wakes up to an empty bed and wonders if he had dreamed the whole event when Kate walks in, bearing coffee for them and wearing only his shirt. They two agree that they want to pursue a serious relationship and that their night together was not a one-time thing.
The two are obviously reluctant to admit that they are finally an item when Castle stashes Beckett in his closet when Martha and Alexis show up unexpectedly and later when Beckett wants to do the same thing when Ryan shows up at Beckett's apartment while Castle is there with her. Castle finally admits his secret to Martha, who says that she knew about them all along as "Mother instincts". Later, he decides to tell Alexis as well and they are both are supportive of the relationship.
The two's new romance at the 12th Precinct, however, is far more complicated. NYPD ethics policies forbid romantic or sexual involvement between employees, and Beckett fears that Captain Gates will use the rule as an excuse to have Castle re-assigned or, worse, leave the precinct for good. So at work, the two officially decide to keep their relationship a secret. As a cover, Beckett claims to be involved with an unnamed mystery man. Ryan and Esposito both attempt to discover this secret boyfriend's identity since she refuses to name who he is. In "Murder, He Wrote"; Ryan finally succeeds when interrogating a suspect who had run into Castle and Beckett while the two were on a secret romantic getaway. However, he decides to keep the secret as well until Castle becomes a murder suspect ("Probable Cause") and Beckett's objectivity to evidence incriminating him becomes an obvious issue. Even then, he decides to only tell Esposito, and the two decide to keep Beckett and Castle's secret romantic relationship a secret as well unless they absolutely must reveal it. In "Swan Song", a documentary film crew catches the two in a romantic moment, but Beckett is able to convince the producers to delete the film before it's sent to Gates.
Season five marks a time when Beckett struggles with her fears about Castle. When he takes her on a tour of his house in the Hamptons, she is chilled by the thought of how many women must have also gotten the tour. ("Murder, He Wrote") As part of their campaign to hide their relationship, Castle has a date with a famous Femme Fatale entertainment reporter. She throws herself at Castle while clad in a bikini, with Beckett catching them in a compromising place. While she claims to believe Castle when he says he would never have cheated on her, she still turns down his advances that night as it was "too soon". The investigation, centering on a local TV news channel, is fraught with references to the dangers of secret office romances. ("Cloudy with a Chance of Murder") But Beckett never doubts Castle himself as we see in "Probable Cause", despite heavily convincing evidence that he has cheated on Beckett and committed a murder to hide the affair (though no one in the precinct really believes the charges, even Gates who is known to dislike Castle).
While their relationship was forged during the time when Beckett has resigned, the two are united by their determination to solve murder cases. This drives Beckett to ask for her job back from Gates in "After the Storm". During their vacation in the Hamptons, Castle becomes fascinated with a murder that occurs near his summer home. Beckett is annoyed and amused that he can't put aside his obsession with solving cases for their romantic getaway, but as time goes on, she is similarly drawn in.
In this season, we see another aspect of their relationship. Over the years, Castle's serious and driven side has often emerged due to Beckett's influence, and the worst of his immaturity has faded. Now, as Montgomery suggested in Season Three, we at last see Beckett's fun side emerges, even as the worst of her obsessiveness and seriousness has faded under Castle's influence. Beckett engages in a romantic cosplay with Castle, dressing as her favorite character from a long-cancelled science fiction show (and with a scary monster mask from the same show added for fun) ("The Final Frontier"). She locks a camera crew that had filmed her in a closet, giving them a playful raspberry as she slams the door shut ("Swan Song").
In the season 5 finale Watershed, their relationship undergoes major decision-making. By then it has become clear Beckett has been offered a big time job in Washington DC, but fails to tell Castle about her grand opportunity. When Castle eventually learns about it himself, he confronts her about not telling him, and they both have a fight. They ask themself and their parents later on; what do they want with their relationship? Beckett eventually, under advice from her father, decides to take the job since it is what she knows she wants. Her decision is also made because she remains unsure of what she and Castle have is truly real or not, where the relationship is ultimately heading and if all they fell in love with is just "the dance" the two have been in and fears what will happen "when the music stops". She calls Castle and tells him they need to talk, to which he also agrees. When the two meet up, she tells him she is taking the job. Castle begins talking about their relationship and how they have never truly defined it and Beckett thinks that they are going to break up. Instead, Castle gets on one knee and displays a ring and asks her, "Katherine Houghton Beckett, will you marry me?" Beckett is left shocked in silence as she simply looks at him.
After last season's big cliffhanger, Kate was initially shocked by Castle's sudden proposal, thinking that he was going to break up with her because he was acting so serious. After an uneasy awkwardness, Beckett admits she got the job in D.C and admits to Castle she does love him, but she doesn't want to miss her shot at the job. However, Castle reaffirms her by saying he was proposing because he couldn't imagine his life without her, not to keep her in the city. With a smile, she says, "Well then, Richard Edgar Alexander Rodgers Castle, yes. I will marry you."
After six weeks, Castle surprises Beckett at her D.C. home and the two have a happy reunion. He also meets her new partner, Rachel McCord. However, his attempts to help in a Classified federal case soon leads him into trouble with Beckett's partner and gets her into trouble at work. As Castle tries to make it up to her, he is inadvertently pulled back in by the suspect Beckett was looking for only to die. However, things take a turn for the worst when Beckett learns that the suspect's car was tampered with to emit a highly toxic gas in his car, Castle is pulled back into the case, all the while Beckett is looking for answers to who did this to her fiancé. While the culprit was caught and Castle was saved, Beckett soon learns that the man that started all of this, a four star general, wasn't going to be investigated due to political blow back.
When Beckett and McCord arrive from D.C. (Need To Know) to take over a case the NYPD and Castle were working on, Castle finds his loyalties divided between Beckett and the boys from the NYPD. While initially Castle, Esposito and Ryan tried pursuing leads, McCord forced them to close the case due to the CIA's involvement, but Beckett managed to give Castle the information needed to catch the killer, showing she still believed in the NYPD and Castle. When the CIA tried to blackmail the victim's girlfriend into helping them, due to her ties to Russian organised crime, Beckett tipped off the press to keep the girlfriend out, seeing what the CIA was doing was wrong. Back at the loft, Castle admits that distance between them was too hard for him and proposed a solution: an apartment in D.C. for him and Beckett. This shows Castle is willing to compromise for Beckett as she was both shocked and delighted by this gesture. However, everything came crashing down when McCord showed up and told Beckett she was fired due to tipping off the press.
In Number One Fan, Beckett becomes frustrated by the fact the NYPD couldn't hire her back because budget cuts and reveals she has not been out of work since she was fifteen. When Capt. Gates calls Castle to assist in a hostage negotiation, Beckett offers to help in the case as well. Gates accepted her help, knowing she was still the best homicide detective around, even without her badge. When Castle was shot trying to defuse a wrestle for the suspects gun, Beckett immediately rushes to Castle's aid, even though his 'Writer' vest saved him. At the end of the episode, thanks to the influence of a politician, Beckett is reinstated back at the NYPD and Beckett explains that Police Commissioner knows about their engagement and they are okay so long as the two remain professional at work.
Behind the ScenesEdit
Andrew Marlowe has always called the Castle/Beckett relationship central to the concept of the series as a whole. He refers to the relationship between the two as "the dance", and has drawn comparisons between it and his wife and fellow Castle writer Terri Miller. He argued that it was becoming increasingly implausible to keep the two apart. He referenced other shows where the unresolved sexual tension was left unresolved for too long, leaving the audience unsatisfied and eventually disinterested in their chemistry altogether. He pointed out that the "Moonlighting curse" (where the show went visibly downhill after the two main characters became involved) stemmed from a variety of causes, on-screen and behind the scenes. Marlowe felt that the model for the show moving forward could still include the lighthearted banter and powerful Fillion/Katic chemistry, using classics such as The Thin Man for inspiration.
Nathan Fillion was a vocal opponent of Castle and Beckett becoming an item. He often referenced the Moonlighting Curse, and felt that the show would lose its magic if the central sexual tension was suddenly released. However, after the events of "Always" his view softened, and he now argues that the first four seasons can be seen as a prologue to the interesting fireworks that come from a relationship between two such different people.
Stana Katic, on the other hand, is an unabashed Caskett shipper. She has always stated an eagerness to see the show's main couple hook up, and was excited about the prospect of the Fifth Season, where the two are finally together. Stana said on an interview with TV Guide, that if the couple didn't get together then she would just grab him, and snog his face off. She showed this movement by holding her hands close to her, like a grabbing action and clicking her tongue. She then burst out laughing because of the strange way she just showed how she makes out.
In addition to the romantic rivals listed above, the main cast have come down one way or another on the Caskett issue.
Alexis Castle has seen her father in many casual relationships, and now mostly avoids allowing herself to become invested in them. However, she also has tremendous respect for Beckett, who she sometimes goes to for advice. The fact that Castle mostly supports this is a sign of the high regard he holds her in; when he was married to Gina, he was resistant to allowing Alexis and Gina to form a relationship.
Martha Rodgers often gives romantic advice to her son. She always urges him to declare his feelings and experience the moment. While she has always liked and respected Beckett and supports a relationship between the two, in recent years their seemingly endless dance, and the emotional toll it's taken on her son, have caused her to begin to urge Castle to make a clear offer to her, and if she rejects, to move on. ("47 Seconds")
Ryan and Esposito's platonic "bromance" somewhat mirrors Castle and Beckett's romantic struggles. Both good-naturedly poke fun at Beckett's obvious affection for her partner and consider Castle to be part of their team. Esposito's first loyalty is to Kate, though, and more than once he's taken her side against Castle.
Lanie Parish is a devoted in-story Caskett shipper and has been from the start. In "Hell Hath No Fury", she explicitly advises Beckett to date Castle. However, she hasn't been above getting Beckett to date other men as well ("The Third Man"). Like Martha, she urges her friend to seize the moment and enjoy life with someone. However, she considers Castle to be Beckett's best match, and repeatedly urges her to make a move before it's too late. Finally, in "The Limey", she lays her cards on the table. In two separate speeches, she tells Beckett that life is too short and uncertain to wait to make a move.
Roy Montgomery, before he died, held both Castle and Beckett in high esteem, and later admitted that he'd ordered Beckett to work with him because he felt that Castle was good for her and made her job more fun. He strongly encouraged Beckett to make a move with Castle in "A Deadly Game". Although he appeared to have engineered their fight in "Knockout", this turned out to have been part of his larger plot to save Beckett.
Victoria Gates, on the other hand, hates Castle, even as she respects Beckett. Forced to accept him back into the precinct after an angry phone call by the Mayor, she continually berates Castle and reminds him of his outsider status. Gates has said that as soon as the Mayor leaves office, Castle will be out. She explains her position to Kate in "Heartbreak Hotel": she feels that Beckett is a gifted detective, but that she would be even better if she could avoid the distractions. She feels that Castle's antics and their personal chemistry are a net loss for Kate's productivity and professionalism. For her part, much, but not all of Kate's friction with the Captain stems from Gates' conflicts with Castle. However, in recent episodes, Gates seemed to, at least, tolerate Castle ideas, knowing even though he has some outlandish ideas, she can not argue with the results that Detectives attain.
- The Cup of Coffee: Prior to Castle's arrival, Esposito was the one who sometimes brought Beckett coffee. Midway through the first season, Castle picks up on Beckett's coffee blend and made it a regular habit to either bring her a cup of coffee from a coffee shop, or make her one from the espresso machine he brought for the precinct. When he doesn't, it's usually a sign that he's considering ending the partnership. Beckett also occasionally refuses the coffee; this is usually a sign that she is angry with him. In "Always", he admits that he does this, so he can see her smile. Starting with their relationship in Season 5, Beckett now sometimes gets Castle the coffee, a sign that his affection is now openly reciprocated.
- The Empty Chair: Beckett has never made a move towards Castle unless he attempts to sever the relationship outright first. Her grief at being without him is symbolized by her looking at the empty chair that he usually occupies next to her desk.
- Finishing each other's sentences: This is a sign of the rapport between Castle and Beckett and is a source of good-natured ribbing for their colleagues. Castle having this rapport with another woman investigator is often a prelude to jealousy from Beckett (e.g. Agent Shaw and Sophia Turner). In "The Limey", Castle intentionally avoids building theory this way with Beckett, and then comments at how out of sync they are.
- "Always": Castle usually uses this following a significant relationship moment for the two, as an answer to a question from her. It refers not just to the question she asks, but to his own devotion to her. Beckett has also used the word from time to time, clearly meaning the same thing.
- "I'm so glad you're okay": When rescuing Castle, Beckett almost always greets him with this phrase. When Castle puts himself in harms way, Beckett is clearly concerned and cares about his well-being.
- "See you tomorrow": In "A Chill Goes Through Her Veins", Castle remarks that "night" is boring, while "until tomorrow" is more hopeful. When either of them is reaffirming their commitment to the relationship, "see you tomorrow" is usually the line they use. When either is expressing dissatisfaction, especially Castle, they say, "good night".
- Closing elevator door: Castle prides himself on his poker face; however, the mask invariably drops for a moment as he leaves the precinct via the elevator. As the door closes, we often see a reaction shot related to his relationship with Beckett.
- Handshake: Due to Beckett and Castle keeping their relationship a secret, while at work they shake hands as a way of kissing each other goodbye.
- Beckett had come close to admitting her feelings for Castle several times. However, in every case it is only when he is about to leave altogether.
- Until her conversation with Lanie, it wasn't clear whether she was interested in him romantically at all, or if she simply valued their friendship so much that she was willing to be his lover, so she could keep him as a friend. Similarly, she might have enjoyed being pursued by Castle because it flattered her ego, even as she realized that he would not be a good match for her to actually be with. In The Limey, Beckett finally admits that she does want a romance, but is scared that having one and it not working would destroy the friendship which she also values.
- Beckett has definitively rejected Castle three times. In two of those cases, he responded by immediately pursuing another woman (Gina in A Deadly Game and Jacinda after the events of 47 Seconds). The third case followed her shooting; it is not clear if in the subsequent months he had any romantic encounters after she stopped talking to him, but before she reunited with him.
- While Beckett is a major fan of Castle's books, she actively avoids admitting this to anyone, especially Castle. Castle himself notices this several times. In Flowers For Your Grave he notes that she's familiar with books that only his hard-core groupies know; in the same episode Esposito repeatedly notices her love of his books. In Little Girl Lost, Beckett complains about the Nikki Heat cover, only for Castle to realize that she must be a subscriber to his fan club to have seen it. In the same episode, her former FBI boyfriend comments on her obsession with his books and how they had helped her get through a very rough time in her life. Both agree that Castle must never know. He's Dead, She's Dead finds her again commenting on obscure Castle trivia (his middle name and its etymology) from his fan sites. In Heroes and Villains, Beckett feigns disinterest in Castle's new graphic novel, only for the comic store owner to express confusion and ask why she reserved an advance copy.
- In the wake of her mother's murder, Beckett became emotionally isolated, unapproachable. Castle's accusation in Knockout that she hides in nowhere relationships with men she doesn't love is supported in conversations with her therapist throughout Season Four.
- Castle's emotional isolation is less obvious but equally present. He too, has hidden in shallow relationships with women he doesn't love.
- This wasn't evident until A Rose for Everafter. Castle was deeply in love with Kyra Blaine, who took a break in the relationship and then never spoke to him again. Beckett described her as "real" and expressed surprise that he would have been in a relationship with her.
- In Pandora and Linchpin, we see yet another relationship with an intelligent and sensitive brunette: Sophia Turner. Their relationship, very similar to Castle's relationship with Beckett, ended after a year. Turner is inconsistent in describing the circumstances under which they parted, and Castle won't describe them at all. In the course of the two episodes, it's revealed that she never loved him at all, and had been using him the whole time.
- There are hints that his relationship with his mother hasn't always been as good as it is now. In Nanny McDead, he explains to Alexis that he didn't get a nanny for Alexis because his own mother had dumped him with a soap opera obsessed alcoholic while she pursued her acting career. It also explains why he is so protective of Alexis—he wants to be the good parent he never had.
- Castle had repeatedly expressed that he had no interest in pursuing the identity of his father, until Sophia Turner's revelation that his father had arranged Castle's CIA connection. It's possible that Castle feared rejection until it became clear to him that his father has supported him all along, albeit secretly. Until then, his dad was yet another loved one who abandoned him.
- In Hedge Fund Homeboys, he explains that he'd been kicked out of a series of exclusive prep schools. And in The Final Nail, he describes being lonely and isolated until Damian Westlake took him under his wing. This suggests a brilliant, but troubled child with no real emotional connections who took refuge in books. His own man-child persona isn't that of a spoiled rich jerk, but someone who is trying to experience a childhood they missed out on.
- Castle has been pursuing Beckett sexually since the pilot, but he's also been reluctant to admit to having real feelings for her. The above gives some perspective on why it was so hard for him to admit that he loves her. The people in his life who he's really cared about have always abandoned him.
- Castle's lack of a father figure has lead to him to surround himself with dominant women. (Both Nathan Fillion and Executive Producer Andrew Marlowe have discussed this dynamic and its origins in detail.) Even Alexis typically acts as the "parental" figure in the relationship. Martha and Meredith are hardly paragons of good judgment, but both have strong, larger-than-life personalities.