In "The Final Frontier" episode of Castle, Becket and Castle investigate a murder at a sci-fi convention. The episode is filled with a ton of references and images that should please comic book fans. Most of the references revolve around Disney-owned properties such as Marvel Comics and the recently acquired Star Wars. In the preview clip below, Richard Castle, who is played by Nathan Fillion, is shown signing copies of his Storm Season graphic novel by Marvel Comics. After taking a stroll with Kate Beckett around the convention floor, they come upon a display booth for the sci-fi show Nebula 9. Here's where Castle drops the Firefly reference. Castle says, "How is Nebula 9 worthy of all this? They were canceled over a decade ago after 12 episodes, which was 12 episodes too many." Beckett replies, "I though you would be a fan." To which, Castle responds, "I'm a fan of good sci-fi…Star Trek, Battlestar, that Joss Whedon show, but Nebula 9, it's all phony melodrama and lifeless acting." Of course that Joss Whedon sci-fi show that Castle references is Firefly, which was canceled over a decade ago and ran for 14 episodes. In Firefly, Nathan Fillion played Malcolm Reynolds, and the show still has a huge fan following even today. Even though Firefly was not a Disney show, Joss Whedon is now under an exclusive contract with Disney. "The Final Frontier" episode of Castle airs on Monday, November 5 from 10:01 PM to 11:00 PM ET on ABC.