Nathan Fillion and Stana Katic, Castle

Nathan Fillion's character on Castle doesn't take many things seriously, something that perhaps has rubbed off on the actor.

When asked what he thinks will lure viewers into the ABC procedural dramedy's second season, the 38-year-old former Firefly and Desperate Housewives star cracks jokes. "This season we decided to go with no hooks, no hooks at all," Fillion tells TVGuide.com. "That's become our mantra: no hooks, let's just coast. One episode, we actually take an episode from the first season and just changed everybody's names and filmed it again."

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Co-stars Stana Katic and Seamus Dever, who join Fillion on the other end of the line for a telephone interview during a break from shooting, laugh at most of Fillion's jokes. All the actors say humor is what sets Castle apart from the glut of other crime procedurals.

"The writers are very realistic about the kind of show that we have," Katic says. "We're a crime procedural, but through a light-hearted, comedic eye. I think the other shows that we reference are kind of dark and try to be very realistic and scientific and pragmatic, and I think we just have fun with it."

Dever is a fan of the show's focus on the nuts and bolts of being a homicide detective. "I think there's a little bit of a post-modern comment on other shows because we come around after America has been exposed to 10 years of CSI," Dever says. "I think we're commenting on what really is police work: pounding on doors and taking phone calls, rather than being about forensics. I think that comes from the police officers and detectives that work on our show."

Check out photos of the cast of Castle

Fillion the jokester can't help but capitalize on Dever's setup. "We hung out with a bunch of homicide detectives, and they're not haunting, they're not brooding, they're not tortured," FIllion says. "They were brilliantly entertaining, and they were incredibly funny. It's just that all their stories start with, 'So this guy gets killed ...'"

Fillion says that playing the class clown is part of the fun of portraying Richard Castle, but Katic says there more to the character than being a cad. "There's a wonderful undercurrent that we get to see when he is in scenes with his mother and daughter. I think you see a real heart that beats there, and I think that as episodes continue, people will get to be charmed by that side as well."

The question on many viewers' minds, however, is when, if ever, Katic's Detective Beckett will be charmed by Castle. Fillion is equally stumped, but says that's what makes Castle's attraction to Beckett fun to play. "One of the things that attracts him so much to Beckett is that he can't crack that shell," he says. "He can't get to that spot, so he keeps chasing her. And she's a real authority figure; no one else really has control over Castle the way Beckett does."

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A guest-starring Debi Mazar (Entourage, Dancing with the Stars) will further complicate the relationship. As Paula Haas, a book agent from Castle's past, Mazar makes Castle an offer he'll find hard to turn down. But it's also one that could derail any hopes of a Castle-Beckett hookup.

About the potential love triangle, Katic is expectedly coy. "Honey, we never kiss and tell. You'll have to watch and see," she says.

So is that to say there is a kiss in the couple's future? Katic is silent. Dever laughs. Cue Fillion.

"I'm always kissing everybody," he says. "I recently sneaked one in with [Dever's] Detective Ryan. It surprised him, that's for sure."

Castle airs Mondays at 10/9c on ABC.