Castle Castle

Viewers are certain to geek out over Monday's Comic-Con-inspired Castle, but not all of the sci-fi nerds in the episode will be those dressed up for the convention. 

Exclusive: Castle recruits Star Trek alum for Comic-Con episode

In our exclusive sneak peek at the episode below, Castle (Nathan Fillion

) and Beckett (Stana Katic), meet Gabriel Winters (guest star Ed Quinn), the former star of the "unjustly" canceled sci-fi series Nebula 9. Since hanging up his boots (and tightpants?) as Capt. Max Richards (wink, wink, Firefly fans), Winters now spends his day appearing at conventions and therefore becomes part of the investigation when a superfan is murdered.But perhaps there is another superfan in the room in this clip. Just look at how Beckett lights up when Winters walks in the room. Does she have a crush on him? Maybe not, but Star Trek: The Next Generation star Jonathan Frakes, who directed the episode and knows a thing or two about obsessed sci-fi fans, confirms Beckett secretly flies her nerd flag.

On the set exclusive: Castle investigates a sci-fi convention murder

"What was fun for me was having Beckett reveal and then try to cover up the fact that she was, like a Trekkie, a huge fan of Nebula 9," Frakes tells "The layering of the conflict with her being a straight-ahead cop and still being a closet fan [provided] great comedy."Watch the clip below. Castle airs Mondays at 10/9c on ABC.