Castle and Beckett’s (Caskett) relationship has a long and complicated history.
In Season 1, the duo develop a working relationship. Castle, having killed off his most popular character, Derrick Storm, begins shadowing the detective darling. Captivated by her charm, Rick decides to base his new character, the sexy and intelligent Nikki Heat, on her.
Later, after noticing that Beckett always wears a man’s watch, Castle discovers Beckett’s big secret: Her mother was murdered and justice wasn’t served. Against her wishes, Castle re-opens the case and she cuts him off. However, she takes him back after a heartfelt apology. Who could say no to those puppy dog eyes?
Season 2 has a different tone for the twosome. They spend most of it bantering back and forth, all the while creating a solid foundation of friendship. When a Nikki Heat-obsessed stalker goes after Beckett, Castle saves her from dying as her apartment goes up in flames — and afterwards invites her to stay at his loft. But before Castle even has a chance, heartthrob Thomas Denning waltzes into the picture and steals Beckett’s heart, albeit only temporarily.
Despite Demming, Castle goes out on a limb and asks Beckett to spend the summer in the Hamptons with him — an offer she politely turns down to have more time with the D-man. But when Castle leaves NYC for the islands, Beckett realizes just how much she cares for the crime writer, breaks up with Demming and vows to tell Castle her feelings. However, Castle, feeling rejected after Beckett turns him down, invites his ex-wife/publisher Gina along in her place, and rekindles that relationship, much to Beckett’s dismay.
At summer’s end (and the beginning of Season 3), Castle returns from the Hamptons and doesn't call the 12th precinct as promised. Beckett and her team are livid with him, but eventually let him back on the squad. That’s when Castle discovers that Beckett broke up with Demming and spent the summer investigating her mother’s case. Unfortunately, she also investigated something else: her new dude, cardiac surgeon and motorcyclist, Josh Davidson. Girl can’t stay single for long!
While all seems peachy on the outside, the truth is Josh doesn't make much time for Beckett, and she knows it isn't going to last. However, she decides to stay with him after he turns down a Doctors With Borders mission to get some QT with her.
Castle, on the other hand, decides to cut off his ex Gina because the “magic” was gone — and he had clearly developed feelings for Beckett. Later, when the first detective who looked into Beckett’s mother’s murder reaches out to her with new 4-1-1, Castle steps up to the plate to support her, despite her warnings to back off for his own safety. Their relationship gets physical when squad members Ryan and Esposito are kidnapped. Castle and Beckett come to their rescue — and share their first “magical” kiss (while posing as a drunken couple to distract a guard so they could ransack a building) in the process.
Throughout Season 3, Castle and Beckett’s friendship blossoms as a result of their teamwork and several shared near-death experiences. As it should.
At the tail end of Season 3, Beckett is shot by a sniper at Captain Roy Montgomery’s funeral, presumably by someone connected to her mother’s murder. Before the brunette beaut goes unconscious, a terrified and forlorn Rick Castle tells her he loves her. But does she hear him? And more importantly, will she survive?
Beckett does survive the sniper shot, and she's a free woman again, having broken up with Josh the Surgeon. But Season 4 begins with Castle and Beckett both harboring massive secrets.
Castle’s secret? He’s actively trying to distract Beckett from her mother’s murder case for her own safety and, perhaps worse, is working on the case himself. As for Beckett? She hasn’t told anybody — besides her therapist — that she remembers the entire shooting … including Rick Castle’s “I love you.”