Cut to Castle playing cards with a bickering James Patterson and Stephen J. Cannell, who are like a less Muppety Statler and Waldorf. Castle tells them the story of the case so far, pitching it as if it's a story he's writing, and both of them are like, "That's it? That's stupid." They say that the lack of fingerprints at the crime scene doesn't jive with the fingerprints on the letter, so this guy can't be the actual guy, and Castle needs a character to dig deeper until he's found the truth. Castle says he's got just the guy. (Hint hint: it's him.)
Becket shows up at the station to find Castle going through her paperwork at her desk. She pulls it away, and he says he came by to give her a gift -- a signed copy of his new book. She seems legitimately touched. He turns on the charm and kisses her on the cheek before leaving. She is taken aback by the unexpected tenderness, sits down, shakes her head and smiles. ...Then she realizes he stole documents out of her files, and storms off in a huff. He must have just barely made it out of the building, because Castle is doing research at a library when Beckett arrives with three patrolmen to arrest him -- his mother told them where he was, of course. As they cuff him and drag him away, he tells Beckett that she has the wrong man -- Kyle, not him -- because the wrong type of flower was used in the second crime scene.
At the station, Alexis and Martha come to pick Castle up, and the captain tells him to stay off the case. Castle tells him he will, but they still have the wrong guy. Beckett goes back to her evidence board, and when a detective asks what she's thinking, she says that the pattern makes no sense (stranger from work, close acquaintance, stranger from work), and the details of the crime scenes are wrong. The dress on the woman in the pool was the wrong color, for example, and Marvin should have been suffocated with a plastic bag, not strangled. Someone who's truly imbalanced wouldn't have been able to not get those details right. This scene cuts back and forth with Castle in the taxicab home, following a similar thread with Alexis. He says that with one murder the cops look for a motive, with two they look for a connection, and with three they look for someone like Kyle -- somebody with motive is trying to throw suspicion off, and set Kyle up to take the fall. Since the killer knew about Kyle's Richard Castle fixation, it had to be someone who knew Alison, who was the only one of the three who was privy to Kyle's illness. Castle and Beckett both think Alison was the target, and the other two were collateral. Martha makes a bizarre comparison to a confusing play she was in. Alexis and Richard ignore her.