Blame it on love. After some exquisitely protracted flirtation, roguish mystery writer Richard Castle ( Nathan Fillion) and keen NYPD homicide detective Kate Beckett ( Stana Katic) are finally exchanging pillow banter in the fifth season of Castle.

And ratings for the ABC series (Mondays at 10 p.m.) have never been better (an average of 14.1 million viewers).

Or maybe it’s not the sex. Because the audience for this intoxicating and unique comedy-romance-crime procedural hybrid has grown every year it’s been on the air.

In any event, this season strikes its star as different. “I feel like it’s a new series entirely,” says Katic. “The tone is lighter now that the two characters are together. It’s a treat to go to work.”

Two side effects of the passion plot line: Fans of the show, determined to come up with a cute pet name for the couple, have settled on the unfortunate “Caskett.”

And the new intimacy means that in many scenes this year, Katic, 34, is wearing less clothing.

“It’s a balancing act to make it sensual and keep it modest enough for network television,” she says. “The other element is I’m protective of the character. She’s the romantic lead, but I don’t want her objectified, especially since our audience is so heavily weighted with females. I definitely want her to be respected.”

This being Castle, even the bedroom scenes can be a little offbeat. In a recent episode, a hot-and-bothered Castle watched as Beckett did a slowly revealing Gypsy Rose Lee dance in a Star Trek-like sci-fi costume (long story). When she finally emerged, she was wearing a hideous alien mask, putting a real and immediate damper on the mood.

So how did this pairing come to be? Fillion was the tent pole of the show, because of his strong cult popularity from roles like Captain Mal on Firefly. The lesser-known Katic was chosen after an exhaustive search because the two displayed evident on-camera chemistry.

Unexpected bonus: Katic’s comic chops, which give the dialogue its distinctive tom-tom rhythm.

But Katic is dour about the couple’s prospects.

“The Castle character has always been something of a cad — very funny, very charming, but as soon as the question of more depth comes up, he bounces,” Katic says. “I wonder if that’s going to be enough for Beckett. She’s starting to think of him as a future husband, a possible father. She’s complex and loving and twisted and all of the wonderful contradictions I think almost every woman is. I think a woman like that is going to demand a partner and a lover with depth as well.”

David Hiltbrand

The Philadelphia Inquirer