Beckett is used to Castle spinning a theory into a story, to the point where even the most sensible explanation loses all credibility, but this has the be the story that tops them all. It's Caffrey's fault, of course; the two of them are egging each other on, each trying to outdo the other's tale, paint the more impressive picture.
She and Burke, artists of a very different medium, watch from across the room. "When are you planning on telling them that we caught the guy?" her companion asks her, sotto voce.
Beckett feigns looking at her watch. "Actually, I'm going to get lunch. If Castle notices I've gone, tell him I'm checking out a 'promising lead'."