When Castle tackles a Comic-Con-inspired episode later this season, the show will have the sci-fi bona fides to back it up.Star Trek: Deep Space Nine alum Armin Shimerman will guest-star as Benjamin Donnely, a tech geek who manufactures authentic props for people's costumes at sci-fi conventions, TVGuide.com has learned exclusively. We hear he'll be a little too eager to show Beckett (Stana Katic) how all his guns work.As we previously reported, Castle (Nathan Fillion) and Beckett end up at the convention to investigate the murder of a fan. While there, the duo will encounter former sci-fi star Gabriel Winters (Eureka's Ed Quinn), whose career fell apart after his cult-favorite show was canceled. Now, he spends his days at fan conventions and nights having drunken one-night stands.Naturally, Castle will have a little fun with Fillion's past on the short-lived Firefly. In fact, Winters used to play Capt. Max Richards, a clear play on Fillion's Capt. Mal Reynolds on Firefly. Additionally, the show has cast Christina Moore (That '70s Show, Hawthorne) to play Stephanie Stern, the actress who played "Lt. Chloe." Unlike Winters, Stern has gone on to a successful movie career.Castle's Beckett made our list of sexiest TV eye candy!Besides his best-known role as Ferengi bartender Quark on Deep Space Nine, Shimerman has also done lots of voiceover work for video games and cartoons. He also had a recurring role on Boston Legal and most recently appeared in an episode of TNT's Perception.The episode, which will be directed by Star Trek: The Next Generation vet Jonathan Frakes, will air later this fall. Castle airs Mondays at 10/9c on ABC.