Nathan Fillion

``Castle,’’ the frisky new ABC mystery series premiering Monday, March 9, casts Nathan Fillion (``Firefly’’) as Richard Castle, a hugely popular mystery novelist who may have just made the worst mistake of his career: killing off Derrick Storm, the main character in his best-selling whodunits.

His publisher (who also happens to be his ex-wife) is deeply annoyed, but Rick — a puppyish combination of Peter Pan syndrome and short attention span — explains that he had just gotten bored of writing variations on the same book over and over again. He’s looking for something completely different, he tells teenage daughter Alexis (Molly Quinn).

And he finds it, courtesy of Detective Kate Beckett (Stana Katic), a buttoned-up New York cop investigating a serial killer who appears to be re-creating murders from Rick’s novels. Recognizing that Rick might bring a unique perspective, she invites him to consult on the investigation, and his author’s habit of viewing real-life events as elements in a story ultimately does help crack the case, after some bickering and bantering between this oil-and-water odd couple.

Granted, as series premises go, a mystery novelist solving actual crimes isn’t exactly the freshest idea in the world, but there’s a reason the show is called ``Castle,’’ not ``Murder, He Wrote.’’

This new series is carried stylishly and confidently by Fillion in what may be the best role of his career to date after a fairly thankless stint as Dana Delany’s philandering husband on ``Desperate Housewives.’’ In fact, Fillion was filming that other ABC series when the ``Castle’’ executive producers scheduled a meeting with him.

``I never do this in a meeting, but I said, `Listen, I am so this guy. This is me. I can do this forwards, backwards and blindfolded. This is what I love to do,’ ’’ Fillion recalls. ``The script just spoke to me. Here’s a guy who is having fun every day, having adventures, getting away with something. That’s what I want my life to be like. In my real life, I sit around a living room and talk to people, so in my work life, I’d like it to be an adventure like Rick Castle.’’

It certainly wasn’t a stretch to capture Rick’s reluctance to grow up, adds Fillion, 37, who admits that his own inner child is still pretty rambunctious.

``When I was a kid we weren’t spoiled with a lot of toys,’’ he says. ``We have a family joke that when we were kids, we had two toys: Legos and a stick. My parents expected us to use our imagination. Now I’m older and have more disposable income, so I look on the Internet and see an electric skateboard that will carry a guy my size 14 miles an hour, and I’m buying that thing. That’s what I use to go down the corner to get groceries.’’

The show gets additional zing from ``Dharma & Greg’’ veteran Susan Sullivan, romping through her scenes as Rick’s madcap actress mom, Martha Rodgers.

``Susan kind of blows in and out of episodes,’’ Fillion says. ``She comes in like a hurricane, does her bit and mixes things up and then blows out again. What is so great about her scenes is that Susan is an actress who just truly understands comedy. Her comedic instincts are phenomenal, so you really get the impression that Martha Rodgers has a life before she arrives into the scene and she has one after she blows out of it. You just get the very real sense that she’s part of a real world that we’re just getting little tastes of.

``One of the things I love most is you get the distinct idea that Castle has a mother who is not very maternal, and yet he has a daughter who is. Rick mothers his mother and is mothered by his daughter.’’

Yet at the core of ``Castle’’ is the prickly relationship between Rick and Kate, and series creator Andrew Marlowe insists that he and fellow executive producer Rob Bowman are in no rush to turn up the romantic heat between these two characters.

``(Rick) is looking for a new main character ... and (Kate) becomes his muse, the new character for his next best-selling set of novels, so he pulls some strings to allow himself to become her unofficial partner on cases,’’ Marlowe says. ``Castle approaches the investigation from the point of view of `What is the story?’ So he brings in a storytelling point of view, whereas Beckett, who is a good cop, is all about the evidence. You have the two of them investigating the crime from different points of view, and their styles and their personalities clash, and that’s where the sparks fly.’’

``I think what you’re really asking is: `Are they going to blow it early?’ ’’ Fillion says. ``No, I don’t think they’re going to do that. I think you’re going to be very happy and very comfortable with the pace at which they do things. I think we all learned a valuable lesson from `Moonlighting,’ in that once (David and Maddie) got together, that show was over. Here, you have two people who are very attracted to each other and have a real interest in each other, but at the same time they are diametrically opposed (to each other) in a lot of different ways that are going to keep them separated.’’