Partnership with CastleEdit
Beckett is a detective with the Twelfth Precinct Homicide Squad of the New York City Police Department, where she worked with fellow detectives Javier Esposito and Kevin Ryan and medical examiner Lanie Parish under Captain Roy Montgomery until he was killed at the end of season 3. In season 4, Montgomery is replaced by Victoria "Iron" Gates. In the pilot episode, Beckett leads the investigation into the murder of Allison Tisdale, which is staged in the style of a death scene described in the Richard Castle novel Flowers For Your Grave, along with other murders based on Castle's fiction.
Beckett is forced to have Castle consult on the case, and though she tries to contain his access, he repeatedly violates police protocol. Although the killer is apparently caught when he leaves his fingerprints on a note he allegedly sent to Castle, Castle convinces Beckett to continue the investigation based on a hunch, the two discovering that the killer was actually Allison's brother, setting up a mentally ill client of his sister—a social worker—so that he could claim the majority of their father's estate due to his father suffering from terminal cancer. By the end of the pilot, Castle uses his friendship with the Mayor to get partnered with Beckett under the pretense of conducting research for a new series of novels starring a detective based on Beckett. Toward the end of the fourth episode, Beckett's literary alter-ego is revealed to be named "Nikki Heat," much to Beckett's annoyance.
Since the explosive season 4 finale, the crime duo have been dating. Castle proposed to Beckett in the season 5 finale when Kate had been offered a job in DC to work for the Attorney General's office.
During the pilot, Castle speculated that Beckett had joined the police force due to an unsolved trauma suffered by someone close to her, and Beckett implied that he was correct. Castle also confirmed that Beckett "does have a history with (an) unsolved crime" which inspires her to build "case[s] that would never fall apart in court." In the second episode, Beckett plied suspect Chloe Richardson by admitting that someone close to her had been killed. By the fifth episode, Beckett tells Castle that it had been her mother, Johanna Beckett, who had been violently murdered, and that Beckett became a cop because she wanted to be a detective who did not commit what she felt was the investigating detective's mistake of "pigeon-holing" crimes (she explained to Castle that she believes that her mother's killer was never caught because the investigating detectives simply assumed that she was killed in a botched robbery and ignored all evidence to the contrary, such as the fact that her mother still had her purse and keys when she was found). She explained that she now wears her mother's wedding ring on a necklace for "the life [she] lost" and her father's watch for "the life [she] saved" when she helped him recover from his alcoholism. She also reads mystery fiction as a result, hoping to gain insight into murderers' motives, and is not so secretly one of Castle's fans, although her main strength as a detective lies in her ability to empathize with the relatives of violent crimes, which she does "better than anyone [Montgomery] knows".
In "Little Girl Lost", Beckett's past is further revealed when a former love interest, FBI Agent Will Sorenson, returns to New York and requests Beckett's assistance on a kidnapping case. It is revealed in the episode by Sorenson that Beckett once waited in line for an hour just to get one of Castle's books signed, and also how his novels helped her through her mother's death. In the first season finale, Beckett angrily refuses Castle's help in reopening her mother's murder investigation—having concluded after conducting her own investigations after joining the force that focusing on her mother's death would destroy her life—stating that if Castle interferes, it will end his police collaboration with her. Despite this, Castle confronts Beckett at the end of the episode with evidence that her mother was targeted for murder. At the beginning of season 2 she forgives Castle for his indiscretion about her mother's murder after he delivers a heartfelt apology. During this period it was also revealed that Beckett speaks Russian after a semester in Kiev between her junior and senior year, as well as spending a brief period modeling when she was seventeen on the grounds that it seemed easier than waitressing (although the only shown photograph of her modeling period is her in tennis gear). Her partnership with Castle is later extended after Castle receives a three-book publishing deal after the success of the debut Nikki Heat novel.
Beckett's mother's case is again brought up at "Sucker Punch" when Lanie contacts a specialist, Dr. Murray, after realizing the wound similarities between the victim and Beckett's mother. Dr. Murray then reveals to Beckett that there is no doubt in his mind, that the victim is killed by the same man that murdered her mother. At first she is informed by a corrupt politician Dick Coonan that it is a contract killer named "Rathborne" that killed her mother and the four other victims. They then set up an exchange—Castle actually donating $100,000 of his own money to cover the fee to fake a hit—so Beckett can finally catch the killer but he never shows. After the exchange goes bust she realizes that Coonan himself is the killer—given that he implied awareness of her connection to "Rathborne" without Beckett having made any reference to her mother's death—and as she goes to arrest and confront him, he takes Castle hostage. Castle manages to free himself but Coonan comes charging after him, only to have Beckett shoot him in the chest, killing him instantly. Though she gains some closure on her mother's death she still must figure out who now ordered the hit on her mother. In the same episode, Castle states that he will stop shadowing her and feels guilty that Beckett had to kill in order to save his life. However, Beckett tells him to stay, admitting that she has grown accustomed to Castle "pulling on [her] pigtails"—although she threatens to shoot him if he mentions that to anyone else—that he makes her hard job more fun, and that she wants him to be there when she finally finds whoever ordered her mother's murder.
Beckett's training officer after leaving the academy was Mike Royce; who according to Beckett was "the only one who understood the obsession that drove [her]". One of their cases involved a karaoke bar; another involved a monkey. She also says that she was in love with Royce, and claims that she was lying by saying it in order to keep him talking on the phone long enough to get a trace. However, after telling Castle that she lied, she walks off with tears clearly visible in her eyes.
In the episode "Knockdown" John Raglan, the detective who investigated in the case of Johanna Beckett's murder, contacts Beckett and is shot by a sniper in front of her and Castle's eyes when he was just about telling them something about the murder. The trace leads to Joe Pulgatti, a mob-boss in the 90's, who was imprisoned for the murder of the FBI agent Bobby Arman. He always claimed to be innocent and told a story about cops who tried to kidnap him, but Arman intervened and was killed by one of them. Nobody believed him till Johanna Beckett, who was killed in the same alley as Arman. This new trace leads to the dirty cops Raglan and McCallister, who was his partner back then. They kidnapped and blackmailed mobsters till this incident with Arman. At the same time Ryan and Esposito traced down the shooter, a contract killer with the name Hal Lockwood who appeared out of the blue in 2004. The two detectives get kidnapped by him and were tortured till Castle and Beckett saved them. Both Lockwood and McCallister were arrested. In the course of this investigation Beckett reveals her home-made murder board for the case to Castle, which she built the summer before.
In the season three final "Knockout" Lockwood kills McCallister behind bars and is breaking free at his official hearing at court. From now on he is hunting down Beckett and it is revealed that there was a third cop in 1992: Roy Montgomery. He shot Arman and he has every single necessary evidence to bring the so-called dragon down. He confesses everything to Beckett and sacrifices himself for her, his last act before dying is killing Lockwood. At his funeral Beckett gets shot by another unknown sniper. While she is lying on the ground Castle finally confesses his love for her.
In the season four premiere "Rise" Beckett barely survives the assassination attempt on her and takes three months off to recuperate. In this time Castle, Ryan and Esposito were tracking the money of Montgomery, Raglan and McCallister, but the evidence was destroyed in a fire in 1998. Beckett doesn't want to believe this, and only after Castle has a long talk to her does Beckett decide to see her therapist again. Castle only talked so seriously to her about this because of a call he received from a mysterious man, who claimed to be an old friend of Montgomery and in possession of the evidence against the dragon and is now blackmailing him in order to keep Beckett safe.
Later in the fourth season, in the episode "Dial M for Mayor" the case surfaces again, but only Castle realizes this thanks to the mysterious man, who informs him that the dragonwants to blame Castle's old friend the mayor with the murder of a young woman in order to get rid of Bob (the mayor) and Castle. Without Castle there would be nobody who could keep Beckett from investigating her mother's case and as soon she does this, the deal between the mysterious man and the dragon is over and Beckett would be no longer safe. The man can arranges for another man who looks guilty to take the fall, but if he is really the murderer is not completely clear.
In the season four finale "Always", Cole Maddox, the man who shot Beckett, returns and tries to find the man, who is blackmailing his employer. Castle tries to talk Beckett out of everything, but as soon he reveals the existence of his mysterious informant Beckett breaks off her partnership with him. Castle is more willing to go than ever before, but he just can't let Beckett throw her life away again. Beckett and Esposito trace down Maddox alone, who defeats both of them and leaves Beckett hanging on the edge of a tall building. In this moment she realizes that Castle is more important to her than justice for her mother. After Gates suspends her and Esposito, she quits and goes directly to Castle. While the two are spending their first night together Maddox visits the mysterious man and threatens him.
In the season five premiere "After the Storm", Castle, Beckett and Ryan manage to trace down Michael Smith, the old friend of Montgomery. When Beckett and Castle find him he is in a very bad shape: Maddox had tortured him to learn where the files are. One of them is burned in Smith's fireplace, another one is hidden in an old storage building. Castle and Beckett head there, but Maddox was waiting for them. Esposito turns up and frees the two out of their hostage situation. Meanwhile Maddox tries in to open the safe with the files, but he is killed by a booby trap and the file is destroyed. The team attempt to reconstruct the files and discover an account number of the senator William Bracken. After they are told Smith is out of surgery, Beckett and Castle go to see him, but he refuses to help them. He is then murdered by one of Bracken's men, though it is made to look like a heart attack. Beckett goes to Bracken and threatens him with the bluff that she has a third copy of the files, and that she is going to publish them if he goes near to her or somebody she cares about.
In "Food to Die For", Beckett becomes reacquainted with her old high school friend, Madison Queller, who revealed that Beckett attended Stuyvesant High School. Madison stated they shared 9th grade French and expressed her surprise that "the biggest scofflaw at Stuy became a cop".
In the series premiere, "Flowers for Your Grave", Castle performs a cold reading of Beckett stating his belief that most smart, good-looking women like her become lawyers and not police officers. He also speculates that she had a good college education and likely had many career options. In "A Dance with Death", Beckett states that she was pre-law atStanford and that she had wanted to become the first female Chief Justice. She was 19 at the time of her mother's murder, which is implied to be the reason for her change in career paths. In "Close Encounters of the Murderous Kind", Castle asks Beckett about her views on deficit spending during difficult economic times and she indicates that she took a semester of economic theory at NYU.
Throughout the series, Beckett demonstrates functional knowledge of a broad range of general topics she has studied, to the point of having ready familiarity with and informed opinions on those topics, even in subjects she did not specialize in during her education or subsequent career, such as literature or economics. Castle occasionally remarks that he finds her intelligent and educated and that his character of Nikki Heat was written to reflect these traits.
In "Under the Gun", Beckett tells Castle that she has a '94 Harley softail motorbike, which she worked through high school to pay for. When he asks why she will not show him a picture of the bike, she says it is because she does not think he could handle the sight of her "straddling it in tight black leather".
In "Last Call", Beckett revealed that she has a tattoo. She also displayed her singing talents with the rest of her team.
In the Season 5 episode "The Final Frontier", Castle finds out that Beckett was (and possibly still is) a huge fan of a short-lived sci-fi series called Nebula 9, so much so that she was part of a Nebula 9 fan-gang in college. Later a picture even shows her dressed up like her favorite character.
In "Heroes & Villains", she is shown to be a client of a famous comic book store, and that she has bought a copy of the graphic novel based on Castle's character Derrick Storm, which she tries to hide as an attempt to help with the sales. When she interrogates Officer Hastings, who has been fighting crime as a vigilante called Lone Vengeance and is suspected of killing a man that knew her double identity, it turns out that the two of them are very similar in that they lost one of their parents when someone murdered them and have allowed that to drive their careers towards the police force in order to make justice. It also turns out that she has a boyfriend who works as a journalist and writes a comic about what Lone Vengeance does. Beckett tells her to stop letting her past define her life. When it is found that Officer Hastings is innocent, the officer and the journalist leave the precinct and kiss passionately as the lift door closes. Castle comments on the similarity between the couple the officer and the journalist make and the relationship between himself and Beckett.
In the season three final "Knockout", after Beckett has been shot by a sniper, Castle tells her that he loves her . In season four premiere "Rise", Beckett says she does not remember anything about her shooting (implying that she didn't hear Castle's declaration) but it is later discovered that she remembers everything that happened that day. During Season 4, Castle discovers that Beckett does remember him saying that he loved her but she can't be honest about her feelings. In later conversations with her therapist and friend Lanie, Beckett is reminded that Castle may not wait for her to return his feelings and she'll be faced with the fact that he's moved on. During the season finale "Always", however, Castle restates to Beckett that he loves her and although they immediately break up their partnership, at the end of the episode, they finally kiss. During Season 5, their romantic relationship continues to be explored.
Beckett's relationship with Castle is strained from the start as she finds him to be annoying and reckless. However, she warms up to him after seeing how useful he is on cases, which he often solves by noticing things that no one else did. The two also begin to develop a strong friendship and to care deeply for each other.
In "Flowers for Your Grave", Castle gives Beckett a brief kiss on the cheek when he gives her an early release copy of his last Derek Storm novel. At one point, Beckett challenges Castle to guess why she is a cop instead of a more stereotypical profession. Guessing that she came from upper middle class, that she lost someone close to her, and that the killer was never caught. Seeing her watch him peg her closer and closer until he finishes, she is obviously bothered by his accuracy. Then, at the end of the episode, he asks her out and when she says no, he says, "It would have been great". She replies, "You have no idea."
In "Nanny McDead", Castle and Beckett are talking about Castle's marriages and Beckett says she's more of a "one and done" kind of girl instead of Castle's two divorces that have already occurred.
In "Hedge Fund Homeboys", for the first time, Becket starts to soften up for Castle by joking with him about all the schools that he was kicked out of and now that he's become famous, they all claim him as an alumnus. Additionally, Beckett is starting to be able to 'read' Castle to know some of his 'looks'.
In "In Her Veins", Beckett first reveals to Castle that it was her mother that was murdered when she was 19 years old and how it happened.
In "Sucker Punch", Castle offers to pay $100,000 of his own money to set up a fake contract with the man who murdered her mother. However, they soon realize that they have been tricked and that the actual killer was someone to whom they had just granted immunity in exchange for the identity of the "real" killer. Castle is taken hostage at gunpoint and Beckett is forced to shoot and kill the suspect before she can find out who hired him to kill her mother. Castle, feeling guilty that she lost her only lead to save his life, decides to end their partnership, but Beckett asks him to stay because, when she finally learns who ordered the hit on her mother, she wants him there with her.
In "The Third Man", Castle observes that being excited about a man is unusual behaviour for Beckett when he notices her playing with her hair while organising a date with a fire fighter Lanie sets her up with. At the end of the episode, Castle and Beckett go to get burgers together as they discuss their boredom on their respective dates. As they walk out the precinct arm-in-arm, Beckett unconsciously plays with her hair, inferring that she is interested in Castle. Further, Beckett only asked Lanie to set her up once Castle revealed he had a date.
In "Tick Tick Tick...", she is shown to be jealous of Castle's attention to Agent Shaw and her high-tech equipment. When Beckett becomes the ultimate target of a serial killer who is obsessed with her being "Nikki Heat", she is almost killed after he blows up her apartment. In order to protect her, Castle allows her to stay with him in his apartment, where she makes him breakfast as a thank you.
In "Love Me Dead", Beckett's relationship with Castle is further demonstrated by Alexis, who looks up to her and sees her as a friend and surrogate mother at times, even (secretly) asking her advice on a foreign exchange program to France. In "Wrapped Up in Death", Castle asks Beckett to look out for Alexis if anything happens to him, which Beckett promises to do. In "Under the Gun", Beckett also dispenses parenting advice, telling Castle that Alexis is entering her "wild-child phase", and jokingly makes references to some rebellious things she did as a teenager, which Castle is very interested in hearing more about.
In "A Deadly Game", Beckett is on the brink of telling Castle about her feelings for him when his ex-wife (Gina) shows up to go to the Hamptons with him, saying he'll "See [Beckett] in the fall". They do not share any communication whatsoever during the summer.
In "Deadly Affair", Beckett and her team find Castle at a crime scene in the season three premiere and arrest him for murder (which she gladly does because he didn't call her to inform that he was back in town), but after he is proved innocent she sets him loose. Beckett (possibly) "loses" a bet with Castle regarding who would discover evidence leading to the next stage of their investigation first- although they both received the evidence simultaneously-, which then results in him being reinstated as her partner.
In "He's Dead, She's Dead", it is revealed that Beckett has looked at the biography page of Castle's official website, and thus knows his middle name is "Edgar". However, his real middle name is Alexander, Castle having legally changed his name from Richard Alexander Rodgers to Richard Edgar Castle (in tribute to Edgar Allan Poe) when he began writing. This could be relevant because the daughter of the murder victim foresaw that someone with the name Alexander will save her life one day.
In "Anatomy of a Murder" Castle is having a discussion with Martha near the end and she states: "Would you be willing to break her out of prison.? Because, that, my boy is True Love." Later, when Esposito and Castle are bantering about being stuck in jail and Esposito says that Castle would have to fend for himself, Beckett says: "Don't worry, Castle. I'd get you out."
In "Nikki Heat", Beckett becomes jealous of the actress Natalie Rhodes (Laura Prepon) (dressed as Nikki Heat, the character Castle based on Beckett) when she sees her kissing Castle in the elevator. Unbeknownst to Beckett, Castle turned Rhodes down, because he felt that she was only acting out a fantasy he created (noting later to Beckett that sleeping with a woman posing as a fictional version of her would be too "meta").
In "Knockdown", Castle and Beckett get involved in a strenuous kiss as a way to distract a guard, but afterwards, it's clearly seen by both their faces and Castle's first comment that they felt something more. Later, during the final gun battle with 'Lockwood', he has Beckett targeted and is just waiting for her to show her face for a head shot. Castle becomes aware of it, sneaks up behind 'Lockwood', and jumps him just as he's about to shoot Beckett. With gusto, Castle knocks him down, giving him 3 hard punches to his jaw, knocking him out. Beckett notes his bravery to save her and is there at the end to help gently bandage his hand.
In "Setup", Castle and Beckett can be seen in a concealed tarp together after being exposed to high levels of radiation. Castle asks Beckett about her recent trouble with Josh (her current boyfriend) and she responds by telling Castle about how Josh has been away a lot, and how she wants him to be there for her. Unfortunately, a man comes and interrupts before Castle can say something to Kate that could probably change their relationship.
In "Countdown", Castle and Beckett are locked inside a giant freezer after raiding the location where a bomb is believed to be held. Fearing that they are both going to die as no one knows where they are, they eventually huddle together to keep warm, but are both very weak from the cold. Beckett thanks Castle for being there with her and Castle replies that he always will be. Beckett touches his face and says "I just want you to know that I...." but passes out before she can finish. Castle tries to wake her up, but he soon passes out as well. However, they are soon rescued by Esposito and Ryan. After finding the bomb later on near the end of the episode, Castle and Beckett realize that it's too late for a bomb squad. Holding hands, they look into each other's eyes and then with less than a second left, Castle yanks all the wires out, miraculously defusing the bomb as the timer hits 0:00. Relieved, he and Beckett hug. At the end of the day, Castle walks to the elevator, leaving Beckett and Josh to themselves. As Beckett is hugging Josh, she looks on at Castle until he's in the elevator. Castle looks completely heartbroken at the fact that they faced certain death twice and yet, neither one of them expressed their true feelings.
In "The Dead Pool", she is "courted" by another writer, Castle's protégé, for information and characteristics. At the end of the episode, Castle admits openly to being jealous, and she turns the writer down, calling herself a "one writer girl". When Castle thanks her, she replies "always".
In "Knockout", Beckett tells Castle he and she are "over" after his unsuccessful attempt to dissuade her from continuing her obsessive pursuit of Hal Lockwood, an assassin connected to her mother's murder. While they fight Castle tells Beckett that he doesn't understand what their relationship is; that they "nearly died frozen in each other's arms", kissed, held hands, and spend their free time together, but they never talk about any of it. He also accuses her of "hiding" in relationships with men she doesn't love. While delivering a eulogy at Montgomery's funeral, Castle sees in the distance the sun reflecting off what he realizes to be a sniper rifle that is aimed at Beckett. Before he can tackle her out of the way, Beckett is shot in the chest. As she's laying on the ground, Castle begs her to stay with him and says "I love you, Kate" before she passes out.
The season four premiere ("Rise") opens with Beckett surviving her injury after undergoing extensive surgery and even flat lining. When Castle visits her, she claims to have lost all memory of what happened and asks him to give her some time to process everything. She takes three months to recover, but doesn't call Castle during that time, in a mirror situation to that of the previous year, when Castle didn't call Beckett for the whole summer. When she comes back to work, she meets her new boss, former Internal Affairs member Victoria Gates, with whom she immediately has a confrontation after she learns that the investigation into the attack on her, as well as Montgomery's death, has been closed. She also learns that, while she was away, Ryan, Esposito and Castle got some information, and that a storage facility possibly holding important information burned down, apparently in an accident. She meets with Castle - who has left the precinct since Beckett isn't there - and tells him that she broke up with Josh during the summer, and that she feels that she can't have an actual relationship while the people that had her mother killed are still free. She attempts to continue the investigation of her mother's death, but Castle convinces her to try and give it some time, so that things may become clearer.
Beckett later confesses to her psychologist that she remembers everything upon getting shot, including Castle confessing his feelings for her, but does not admit this to anyone else. She refuses to pursue any relationship (including with Castle), until the man behind her mother and Roy Montgomery's deaths has been caught. In "Eye of the Beholder", Beckett is upset when Castle becomes interested in another woman, Serena Kaye, but refuses to acknowledge her feelings towards Castle, leading her psychologist to question whether she's worried that he will wait or that he will not.
Castle becomes worried about Beckett when they are working on a sniper case ("Kill Shot"), and realizes that she is suffering from PTSD from her shooting. He begs Esposito, who also once suffered from PTSD, to help her overcome it. To do so, Esposito has her hold the type of gun she was shot with and tells her that she has to make what happened a strength instead of a weakness. Later on, knowing that Castle was the one who talked Esposito into helping her, she thanks him.
In "47 Seconds", Martha encourages her son to tell Beckett how he feels; however, while Beckett is interrogating a suspect, she says "I was shot in the chest and I remember every second of it", not knowing that Castle is in the observation room and overhears it. Castle is stunned and hurt that Beckett has been lying to him the entire time about not remembering anything. He tells Martha that since she never said anything, he believes that it means she doesn't feel the same way. Although Martha believes that he should end his partnership now that he knows the truth, Castle decides to stay on the grounds that he wants to continue, as he wishes to feel he is doing something that matters.
In "The Limey", Beckett and Lanie talk about Castle, leading Beckett to admit her feelings for him. Her attempt to tell him about this (encouraged by Lanie) fails, though, as he appears with a flight attendant at the crime scene. Beckett is disappointed, but still refuses to talk to him about this.
In "Headhunters", Castle teams up with Detective Ethan Slaughter, clearly avoiding Beckett. She talks to her therapist about this and he suggests that maybe Castle is not ready to wait for her anymore. Beckett is devastated to hear this and is therefore happy when Castle ends his brief partnership with Slaughter.
In "Undead Again", the case Beckett and Castle are working on partly mirrors their own problems such as one witness claiming not to remember anything of a murder. In the end, Beckett tells Castle that she is seeing a therapist and is working on herself which causes the wall inside her to slowly come down. To this revelation, Castle says "I'd like to be there when it does" to which Beckett replies "Yeah, I'd like you to be there, too".
In the Season 4 finale, "Always", Beckett and Castle are forced to deal with their relationship when a murder they are investigating turns out to be linked to Beckett's shooting almost a year before. Castle, trying to get Beckett off the case, tells her he loves her and admits that he heard her saying she remembered everything. She is, however, angry that he hid important facts from her in order to protect her and refuses to back off from the case, causing Castle to end their partnership. Beckett is unable to resolve the case this time, though, and, in a near-death experience, realizes how much Castle means to her. After she resigns from her job, Beckett visits Castle, tells him she is sorry and, after some hesitation on Castle's part, they kiss passionately and Beckett takes his hand and leads him to his bedroom.
In the Season 5 premiere, "After the Storm", Beckett and Castle have consummated their relationship when Castle wakes up in his bed the next morning to find a semi-clothed Beckett walking into his bedroom with coffee. They speak about their night, with Beckett asking Castle if he liked it, to which Castle replies with a yes. They both agree that it was not a one time thing, but their conversation is interrupted when Castle's mother comes home, causing Beckett to do a secretive "Walk of Shame" out of Castle's loft, so that Martha and Alexis don't see her.
In "Cloudy with a Chance of Murder", a suspect tells Castle and Beckett about the problems with secret romances and Beckett becomes concerned about having to lie to everyone about their relationship. To make things worse, a woman with the TV station invites Castle to dinner with her. Even worse, she goes to Castle's apartment to get it on with him and is only wearing her bikini beneath her clothes. Castle accidentally butt-dials Beckett and based on what she hears, she breaks into Castle's to find the girl on top of Castle.
In "Secret's Safe with Me", Martha reveals to Castle that she knows about Castle and Beckett. Castle then tells Alexis as well (off-camera). Near the end of the episode, Castle and Beckett share a romantic handshake "kiss".
In "Murder, He Wrote", Castle and Beckett decide to go to the Hamptons for a weekend. While they're there, they are about to go skinny-dipping in his pool and Beckett even fully drops her towel … and then a nearly dead murder victim stumbles in, falling into the pool and drowns. Later in the episode, Ryan finds out about their relationship and keeps it from Esposito. Among other things, Castle speculates to Beckett that since Brad and Angelina are called 'Brangelina', Castle thinks that they should be called "Caskett".
In "Probable Cause", Ryan tells Esposito about Castle and Beckett. Assumedly, Esposito tells Lanie off-camera also.
In "The Final Frontier", Beckett and Castle are called to a Sci-Fi convention.
In "Swan Song", During the video-taping of a documentary about an up-and-coming rock band, Castle briefly caresses Beckett's face and is caught on tape ... which might be fully reviewed by Capt Gates before it's released for publishing.
In "After Hours", Castle and Beckett have a dinner for their parents and themselves which goes VERY badly and only a call-away for a murder seems to save them from a dinner gone bad. This leaves them thinking that maybe they are too different for each other. Fortunately, events bring them back together and even their parents seem to have established a friendship.
In "Secret Santa", Beckett reveals to Castle that ever since her mom died, she and her dad don't celebrate Christmas anymore. However, at the end of the show, she relents and attends the Christmas dinner with Castle and his family when Castle says it's a good time to create new traditions.
In "Significant Others", Castle's first ex-wife Meredith stops by and moves in so that she can help take care of Alexis. This happens while Beckett is there and she is (secretly) hoping that Castle will say no. But, he says yes. This causes a lot of problems between them. Later in the episode, Meridith invites Kate to dinner. Castle is advised by Ryan and Esposito about how bad this can be for him. The girls really hit it off in their get-together and apparently, some secrets about Castle are revealed to Beckett. They leave on good terms, but Meredith tells Beckett that she finally left Castle because he was so unwilling to reveal inner secrets to her. This leaves Beckett wondering.
In "Reality Star Struck", Valentine's Day is coming up. Castle, in an attempt to surprise Beckett, puts a nice gift of a pair of beautiful earrings for her in her coat pocket, not realizing that it is actually Capt. Gate's coat pocket, -- with a note from Castle to Beckett. Fortunately, the note only says, "You are Beauty Passion, and fierce Intellect. Be my valentine. Rick" and therefore, Beckett is not in trouble. At the end, it turns out that Beckett's gift for Castle is a drawer in her dresser just for him.
In "Target", Alexis and another girl are kidnapped and Castle assumes that Alexis was taken because she was at the wrong place at the wrong time. However, Beckett soon finds out that Alexis was the real target. When Castle goes to rescue her, Beckett fears for his life and when he returns back home with Alexis, she tells Castle to never scare her like that again.
In "Scared to Death", at the end, when Castle and Beckett are toasting their success, she tells Castle that she knows this trick with ice cubes. This is probably referring back to the trick she was talking about near the beginning of episode "Poof! You're Dead". Plus, Castle's Bucket List indicates that his #1 is "Be with Kate". He says he put that on about 3 years ago. This also might link to that same older episode because during that episode, he officially breaks up with Gina.
In "The Lives of Others", Castle is at home with a broken kneecap and witnesses what appears to be a murder across the street at another apartment. Throughout the episode, he seems to be gathering more and more incriminating data, but Beckett, Esposito, and Ryan check on things at different times and cannot confirm what he saw. Ultimately, it turns out that it was a birthday present (he was born on April Fools' Day) and Beckett had her crew and Castle's family setup the entire thing on him in order to spring a surprise birthday party for him.
In the season 5 finale, "Watershed", Castle proposes to Beckett.
In "Little Girl Lost", FBI agent Will Sorenson (Bailey Chase) turned up and were found to be Beckett's ex-boyfriend who dated her for 6 months, but broke up with her when he decided to go to Boston for his career. He asked Beckett to go back to him in the episode, Beckett answered that she "would consider it", but it was not mentioned again.
In "Death In the Family", Sorenson was in the car driving former mobster Jimmy Moran back to the safe house when the killer pulled up next to them and shot both Moran and Sorenson. Beckett later looked genuinely concerned at the news of his injury and waited at the hospital with Sorenson until she had to leave for work purposes, returning at the closing of the case laughing and enjoying her conversation with her ex-boyfriend.
In "Den of Thieves", Beckett meets robbery detective Tom Demming (Michael Trucco), to whom she instantly takes a liking. It is later revealed that the two have started dating, eating together at work, and even sharing a cab. At the end of "Overkill", she shares a kiss with him, confirming that they are now in a relationship. However, in the season 2 finale, Beckett breaks off the relationship, claiming that it "isn't what [she's] looking for right now." Demming asks her what she is looking for and she merely looks away.
In the last scene of "Punked", Josh (Victor Webster) comes to the precinct and picks Beckett up to go motorbike riding (shown by her going to get her helmet). Prior to this, Beckett had not told anyone that she had a new boyfriend. In the next episode it is revealed that Josh is a biker and a cardiac surgeon.
In "Last Call", Beckett tells Castle that she and Josh had just been tucked up in bed with her laptop when his call came through to meet him at "The Old Haunt".
In "Knockdown", Castle arrived at Beckett's apartment and asked for Josh before he handed her flowers. Supposed this may suggest that Kate and Josh are possibly serious.
In "Countdown", Josh stays in Manhattan, as opposed to going to Haiti, causing Beckett to think they "have a chance." Josh saves both her and Castle from hypothermia. They embrace at the end of the episode, but Beckett seems distracted and longingly stares after Castle as he leaves.
In "Rise", Beckett reveals to Castle that, sometime during her shooting recovery, she broke up with Josh. She later explains to him that even though she really liked him, she can't be the person she wants to be in a relationship until she has full closure on her mother's murder.