Ryan shows the team the evidence that was found with the murder victim on Castle. "A Murder Is Forever" is the eighth of the show's sixth season.
Added:
Beckett & Ryan examine a murdered woman on Castle. "A Murder Is Forever" is the eighth episode of the show's sixth season.
Added:

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.