Tom Demming as Nikki Heat's close combat trainer with benefits, Don: On Heat Wave, Nikki acknowledged to herself that her relationship with this guy is the kind that goes nowhere after an interview with a potential suspect. On "Food to Die For," Castle himself told Madison that she's with some guy he doesn't see "going anywhere." Is it really a coincidence that we first met Tom in the gym, and that they end up sparring later on so she can get interrogate him unknowingly?

Beckett choosing Castle over Demming in the finale: On Heat Wave, Heat gave in to her instinct and attraction, decided to give Rook a chance to see where it goes. On the finale, Beckett chose to break up with Demming, possibly because she's not as emotionally invested in their new relationship, as she would have been with Castle. She saw him as the safe, stable guy, but with not much passion, at least on her part. On Heat Wave, Nikki also mentioned that Rook gets her heart racing before they even get intimate. With the trainer, however, she needs the physical demands of combat training first before it happens. On "Food to Die For," Beckett implied that Castle "makes her feel alive," and that's even without any physical intimacy between them.

Wonder what Rook was doing in the same house as that murdered woman.