C'mon," wheedles Earl Brooks' alter ego. "You've been a good boy for a long time."

For most middle-aged men that naughty inner voice is urging them to take a drink, buy a motorcycle or visit a massage parlor. The voice in businessman Earl Brooks's head is urging him to kill.

"Mr. Brooks" is about a pillar of the community who moonlights as a serial murderer known as the Thumbprint Killer. He's played, quite well, by perennial good guy Kevin Costner.

But Costner's casting is just one of the film's sneaky surprises. The movie also introduces standup comic Dane Cook in his first big dramatic role ... and he's spectacular. And William Hurt is a creepy hoot as Marshall, the dark side of Mr. Brooks' personality, who is always trying to lead this respected civic leader, husband (Marge Helgenberger plays the Missus) and father to ever more reprehensible crimes.

The downside of writer/director Bruce A. Evans' tremendously ambitious effort is that like its protagonist, "Mr. Brooks" has a split personality. It's really two movies...one quite good and the other quite conventional.

The good movie is a harrowing character study of Brooks, a man whose life is so safe and ordered that he drives a Volvo and lives and works in sterile environments that seem to have been hermetically sealed. His hobby, making ceramics, is uncharacteristically messy. But that high-tech kiln out in the guest house is awfully useful for destroying incriminating evidence.

Evans has directed only one other film (1992's forgettable "Kuffs"), his resume high points being the screenplays for "Stand By Me" and "Starman." But he seems to have studied the brooding works of French master Claude Chabrol; at its best "Mr. Brooks" exudes a Chabrol-like sense of cool detachment and a matter-of-fact approach to the ghastly.

As the film begins Brooks has sworn off killing. Before long his resolve crumbles beneath Marshall's cajoling and insults, and he suits up to kill a young couple he marked months before as likely targets. But the murders are witnessed by a young man in a nearby building, a photographer (Cook) who has spent weeks snapping shots of the lovers through their open bedroom window.

Now this creep blackmails Brooks - not for money or a job at Brooks' company, but for the right to accompany the killer on his next midnight ramble. Cook is completely reprehensible as this thrill-seeking degenerate beside whom Brooks looks like a paragon of virtue.

Unfortunately, a big chunk of the film is devoted to the police detective (Demi Moore) who's obsessed with catching the Thumbnail Killer.

If the scenes of Brooks and his family are rooted in a domestic reality (a twisted domestic reality, but still ... ), the police procedural part of the movie is pure Hollywood hokum. Moore's Detective Atwood isn't just any cop ... she's a millionaire heiress. She has a boy-toy ex-husband who's suing for half her fortune. To further complicate matters, Atwood is being stalked by an escaped murderer she once sent to jail.

While the Brooks plot and Atwood plot eventually dovetail, for much of the movie they're at odds. I'd dearly love to see "Mr. Brooks" re-edited to eliminate the Moore section ... now that would be an interesting movie.

Still, there are flashes of near-greatness here.