The relationship between Richard "Rick" Castle and Katherine "Kate" Beckett. Their relationship has always been complicated. At first, they were just partners at work, but then they became friends and got closer.
Later on, they started to have romantic feelings for one another. It is noted that they were quite possibly in love with each other, but they were too afraid to say it to each other.
Kate realised she had feelings for him in the Season 2 finale. She refuses his invitation to the Hamptons, but when he tells her that he wasn't going to shadow her anymore, she questions her feelings for him. She breaks up with her boyfriend, Demming. When he asks what it was that she wants, she merely looks away. End of the episode, she decides to tell Castle how she feels, as well as accept his invitation, when they're interrupted by Gina, Castle's ex-wife. She soon learns that Castle asked her to Hamptons, and that she accepted. As they walk away, Kate looks on, and suddenly asks 'See you in the fall?' to which he spontaneously replies: See you in the fall.
In Season 3, Beckett is angry as Castle didn't call her after he got back. She is shown to be jealous of his ex-wife, Gina, who was his then girlfriend. In a later episode, Josh Davidson is introduced as Beckett's mysterious, good-looking, motor-cycle-riding doctor boyfriend. Castle and Kate face death more than once in the two-parter, this season. As Josh hugs her at the end, she seems distracted, looking at Castle longingly as he walks away. In 'To Love And Die in L.A', her former partner, Royce is killed for which Kate and Rick go to L.A. Kate and Rick talk in their hotel room, and they almost take their 'partnership' to the next level, when Beckett abruptly gets up and walks into her room. She leaves her hand on the knob, and it is shown that Castle waits on the other side of the door expectantly. She opens the door, just to see Rick's door being closed.
The Season 3 finale, Knockout had them fighting about her involvement in her mother's case. Rick, worried about his partner, asks her to back away from the case, and to think of her father, Josh, everyone who cares about her. To this she says 'And what about you, Castle?' He tells her that she is 'hiding, the same way she is hiding in nowhere relationships with men she doesn't love' .Castle says that he didn't know if they were partners, best friends or something more. The argument gets heated, with Beckett having the last say in it. 'You know what we are, Castle? We are over' . The Captain, a well-trusted and loved man, Roy Montgomery is killed by the people who killed Kate's mother. At his funeral, Beckett is shot, seconds before Castle could take the bullet for her. he holds Beckett in his arms, saying 'No, Kate, stay with me, Kate. Kate, I love you. I love you, Kate'. The episode ends.
In Season 4, Castle is angry as Kate doesn't call after getting back from the hospital. She says she doesn't remember the shooting, to which Castle is disappointed. It is important and should be noted that Kate and Rick are masters of subtext. They talk on the swings, where Kate tells him that she broke up with Josh. She tells him that after her mom died, she built up a wall around her, and hence, she can't be in the relationship she wants to be in until she solves her mother's case. Castle takes this well, and they continue being partners. Beckett is shown to be jealous of all of Castle's admirers more openly. However, in '47 Seconds', while Kate interrogates a suspect, she tells him that she was once shot, and that she 'remembers every second of it', unaware that Castle was listening to what she was saying outside the box. Castle distances himself from Beckett, much to her confusion. She tries several times to tell him she's ready, ready to move on from her's mother's murder, as well as the shooting, but Castle always seems unavailable. In an attempt to move on, he appears interested in an airhostess, towards the end of Season 4. He also shadows another detective, Slaughter, much to Beckett's dismay. Thankfully, this doesn't last long. In the Season 4 penultimate episode, 'Undead Again', Kate finally gets her chance, and tells Castle of her therapy, and how she's 'almost where she wants to be'. When Castle asks where that would be, she answers saying, 'In a place where I can finally accept everything that happened that day-Everything.' referring to both the shooting as well as Castle's declaration of his love for her. Castle tells her that he'd like to be there for her, to which she replies, 'Yeah, I'd like you to be there too' and the episode closes. In the Season 4 Finale, Castle asks Beckett out on a date, and she accepts. Their 'friendship' is later tested, however, when Kate learns that Castle had been working on her mother's case since her shooting. She gets angry, and Castle finally tells her he loves her. (when she is fully conscious) He asks her not to pursue her mother's case as it had proved to be dangerous more than once. She disagrees and they end up fighting, causing Castle to leave with 'Yeah, you're right Kate, it is your life, its okay if you want to throw it away, but I'm not going to stick around much. So this is over. I'm done.' Later, Kate gets into a physical fight with an Cole Maddox, a man involved in her mother's murder, as well as the one who shot her. He throws her over the roof of a building. As she hangs on for dear life, she thinks of nothing but Castle, and refuses to leave the world without him knowing she loves him too. After Ryan saves her, she resigns, and goes to Castle's house. She kisses him, saying 'He got away, and I didn't care. I almost died, and all I could think about was you. I just want you.' They make out passionatelt against the door, and Kate is shown leading Rick back into his bedroom. Caskett has been established. Andrew Marlowe, the creator and executive producer (read almighty God) confirmed that they are togther.
Status: Friends, in love with, had sex, kissed, and boyfriend/girlfriend.