Fool Me Once - S2-E4
Ryan: You know what I don't get?
Beckett: Mm-hmm?
Ryan: Why go to so much trouble to create such an elaborate scam? Fletcher must have spent weeks going through all the prep work.
Beckett: I can give you 50,000 reasons why.
Castle: Yeah, but for con men, it's not just about the money. I mean, for them, it's about the game. The... The thrill they get from pulling a con, it's like a drug high.
Montgomery: [approaching] Con man was on drugs?
Beckett: No, sir. Castle is just giving us psychological insight based on his extensive experience as a fraud.