Knockout

An assassin with knowledge of the details behind Beckett's mother's murder escapes from custody during his arraignment, leaving Castle and Beckett to track him down. Secrets are revealed about Captain Montgomery's past as the third cop. Montgomery leaves evidence of the involvement of a powerful third party in the case for Beckett, before confronting the assassins. He is shot and killed in the process. At Montgomery's funeral, Beckett is shot in the chest by a sniper. Castle tells her that he loves her as he holds her in his arms just before her eyes close.