Fillion and his co-stars revealed several other spoilers about the fourth season.
- The Captain did not send the letter to Castle. Shortly before his death, Captain Montgomery (Ruben Santiago-Hudson) wrote a letter explaining his crimes and everything he knew about the person who killed Beckett’s mother. Fillion reveals that the letter was not sent to Castle. When the panel’s moderator said he was certain Castle received the letter, Fillion said, “You’d be wrong. Spoiler alert.”
- The Season’s second episode will have a superhero theme. There will be masked vigilante and scenes that take place in a comic book store.
- There will be a Halloween episode.The precinct will investigate a case that will be a homage to the film “Ghostbusters.” Said Molly Quinn (Alexis), “It’s going to be someone that vanishes and reappears,” not an actual ghost.
- The triple killer will be back. The murderer who Beckett and Castle could not catch will be back. Last time he appeared, he stole Ryan’s gun and badge. Dever shares, “It’s sort of a big deal that that seed was planted… I think we’re going to see a crime being committed and Ryan’s gun being used. It leads to this whole big thing for Kevin Ryan to get some redemption.”
- Ryan will get married. Detective Ryan’s (Seamus Dever) wedding to his girlfriend Jenny, will create a little rivalry between Castle and Esposito (Jon Huertas). Said Dever, “There’s going to be some wedding planning involved. And some possible fighting over who’s going to be the Best Man. Fillion sticks up for his character: “For a proper bachelor party to be had, one would have to have access to women, fine establishments, and near unlimited funds.”
- Alexis and Castle’s relationship will become strained. “She’s going to be voicing all of her opinions this year,” explained Molly Quinn. “At first [Castle] was just playing around. Now he’s enjoying chasing down killers. He’s getting involved at more than a superficial level with this woman. Alexis, I don’t know if she’s too happy with that to be honest.”
- Beckett’s boyfriend Josh will be back. Josh (Victor Webster), the seemingly perfect doctor who was romancing Beckett, will return. He and Castle will end up in a physical altercation. Fillion said that getting shoved by the tall Webster, “Rocked my brain. I didn’t know what time it was. I didn’t remember my name. I’m going to spoil just a little bit. [Esposito] got between us.”