Castle and Beckett have a major disagreement in this scene from "A Murder is Forever." It has to do with Linus.
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Yes, a murder is forever. So is a diamond. Watch the official ABC promo for this Castle episode now.
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Castle Season 6 Episode 8 Quotes

Castle: You see, I'm honoring you by inviting you into my territory and Linus is part of that territory.
Beckett: And if you want to be invited into my territory again, you should probably rethink that.

Beckett: There's been a murder.
Castle: Yeah, of Linus' feelings.