Beckett: It's not your fight.
Castle: The hell it isn't. I don't hang around you just to annoy you. I don't ride out to murder scenes in the middle of the night to satisfy some morbid curiosity. If that's all this was, I would've quit a long time ago.
Beckett: Well, then why do you keep coming back, Rick?
Castle: Look, I may not have a badge, unless you count the chocolate one that Alexis gave me for my birthday, but I'll tell you this... like it or not, I'm your plucky sidekick.
Beckett: Plucky sidekick always gets killed.
Castle: Partner, then.