Castle, Season 3

[When Castle tells Montgomery his concerns about Beckett]

Montgomery:
Castle, did Beckett ever tell you how we met?

Castle:
No.

Montgomery:
I was working late one night, went down to archives to locate some old reports, and there she was with a flashlight and a bankers box open on her lap, studying this unsolved. She was a patrol cop then, she wasn't even authorized to be down there. When I asked her what the hell she was doing, she told me this was her mother's case. And she'd found some things that didn't add up. Now, I could've written her up right then.

Castle:
Why didn't you?

Montgomery:
Because I knew it wouldn't stop her. It was there in her eyes, man. And I thought, "With this kid's tenacity and some training, I mean, she'd make a hell of a Homicide."

Castle:
That tenacity's gonna get her killed.

Montgomery:
I cannot make Beckett stand down, Castle. I never could. And the way I figure, the only one who can is you.