Castle Castle

The case on Monday's Castle (10/9c, ABC) hits a little too close to home.

Fall Preview: Get scoop on your favorite returning shows

That's especially true for Detective Ryan (Seamus Dever

), who last season lost his badge and service weapon to the 3XK serial killer. Now, the missing gun has turned up — as the weapon that murdered the team's most recent victim."It's a very emotional episode for Detective Ryan," creator and executive producer Andrew W. Marlowe tells "If you're a cop and you've lost your gun to somebody, and then it's used in a murder, the case becomes deeply, deeply personal to you.  It's every cop's worst nightmare, so Ryan is wrestling with the emotions of his worst nightmare coming true. And he's trying to be a good cop in the middle of it and resolve the situation."However, Ryan isn't the only one wracked with guilt. After all, Castle (Nathan Fillion) was with Ryan when 3XK got away the first time. "The fact that they didn't get the drop on the guy, and that the guy's still out there, haunts Castle," Marlowe says.

Castle boss: Castle and Beckett's new secrets are a "ticking bomb"

As for Ryan, Dever says he's thrilled to get a meatier story. "The idea of his badge and his gun affecting someone who is sort of an innocent affects Ryan deeply," he says. "It's nice to explore that side of Ryan. We do a lot with the comedy, so it's nice to actually deal with the serious side of the consequences."In fact, Dever says he thinks viewers will see a slightly more serious side of Ryan throughout the season.  "I've always played it that Ryan was the young guy on this team of very experienced homicide detectives," Dever says. "This year, I'd like to see some maturity come in Kevin Ryan. Maybe a little bit more confidence, maybe a little bit more swagger as a result of being around for a while. He's not the new guy anymore."Dever says the change in his character may also be reflective of losing his Captain last season (R.I.P., Capt. Montgomery!)  and adjusting to the leadership style of Capt. Gates (Penny Johnson Jerald).

Castle Season 4: What happens after "I love you"?

"I think we've all lost a little bit of our innocence," Dever says. "There's a sense of not necessarily trusting someone in authority anymore. I think Gates coming on the horizon is like, 'Oh, there's this new person.' We thought we had everything all cozy and a great relationship, and now maybe work isn't necessarily the best place to spend your time."So why not make your life better outside of the precinct. That just may happen, as both Marlowe and Dever hint that a wedding may be in the works for Ryan in the winter. "Whether we get to the wedding or not is always sort of subject to network approval," Dever notes. "But we're going to a romantic episode every year. Last year was the Nikki Heat one where Ryan proposed to his girlfriend. So I think this year, would be a perfect time for a wedding."Castle airs Mondays at 10/9c on ABC.