As a movie, "21" doesn't exactly add up. But who's counting? (Besides the movie's blackjack players, that is.)

Certainly not most audiences, who are likely to view this slick fictionalization of the best-selling "Bringing Down the House" as the cinematic embodiment of the ultimate "What happens in Vegas ..." fantasy. (Except maybe the part about getting pummeled by a nasty casino enforcer.)

Then again, most audiences don't know Las Vegas. Not the way we do, anyway.

All they know is that magical, neon-lit dreamscape known as Vegas, baby.

And for those besotted by visions of Pair-a-dice, "21" serves up a suitably starry-eyed account of a young dreamer who dares to challenge the forces of darkness. And wins -- for a time.

Its source material recounts the true-life tale of math-whiz students at the Massachusetts Institute of Technology who took their card-counting expertise to Las Vegas casinos and won millions of dollars at blackjack.

That happened in the '90s, but "21" is set in the here-and-now, making certain elements -- especially a key character -- not only exaggerated but downright outdated. (We'll get to him later.)

First, however, let's meet our hero: Ben Campbell ("Across the Universe's" earnest, affable Jim Sturgess), a model MIT student wondering how he's ever going to find the money to attend Harvard Medical School.

Not by earning $8 an hour at a men's haberdashery, that's for sure.

But Ben discovers something easier, and certainly a lot more exciting, than winning a scholarship when his knack for numbers attracts the attention of professor Mickey Rosa (Kevin Spacey, doubling as a "21" producer, in ace snake mode), who invites him to sign on as the newest member of MIT's clandestine, card-counting blackjack team.

Initially, Ben seems reluctant to join the club. He is, after all, an honest, all-American boy. But card-counting isn't illegal. And after comely, come-hither member Jill Taylor (a slyly alluring Kate Bosworth) convinces him to play along, Ben discovers the joys of jetting off to Vegas every weekend, donning disguises, living the high-roller life and, best of all, beating the casinos at their own game.

Enter security consultant Cole Williams (a hard-boiled Laurence Fishburne), an old-school enforcer in a high-tech world, who reacts to the MIT team's tricks with hands-on, in-your-face force.

And that, according to a lot of folks who know a lot more about gambling than I ever will, makes Williams a walking, talking anachronism -- albeit a menacing one -- in a movie supposedly set in contemporary Neon Nirvana.

But that's all part of the Vegas fantasy "21's" selling, along with an utterly by-the-numbers morality tale we know by heart: the temptation, corruption and ultimate redemption of an innocent.

Yes, folks, it's our old pal "Faust," with Ben as the sell-his-soul-to-the-devil opportunist -- and Mickey as the modern Mephistopheles all too willing to exploit a brilliant student's talents for his own ends.

As you might expect from a movie named after the game of chance it celebrates, "21" plays much better when dealing with Ben's temptation and corruption.

In adapting Ben Mezrich's book "Bringing Down the House," screenwriters Peter Steinfeld ("Analyze That") and Allan Loeb ("Things We Lost in the Fire") deploy time-honored caper elements as "21" takes us behind the scenes of the team's card-counting methods, from code words to gestures that signal everything from a hot table to get-out-now trouble.

Thanks to a kinetic (sometimes hyperkinetic) visual approach, director Robert Luketic ("Legally Blonde") and cinematographer Russell Carpenter (an Oscar-winner for "Titanic") inject undeniable vitality, even some welcome suspense, into the essentially static process of watching a bunch of people sit around, place their bets and play their cards.

Eventually, however, the familiarity of "21's" gamble stops paying off, as Ben succumbs to the lure of life as a Vegas high roller -- and the challenge of proving he can stand on his own, without his manipulative mentor calling the shots.

And, as "21" rolls inexorably toward its melodramatic conclusion, it can't help but cheat, glossing over crucial character conflicts and piling on plot twists even less credible than the nightly outcome of the "Sirens of TI" pirate battle. Or a Hard Rock Hotel high-roller suite overlooking Caesars Palace. (Like all too many made-in-Vegas movies, "21" shows a total disdain for local geography. Not that anyone except us locals would notice.)

Yet even as "21" becomes more desperate (and less convincing) by the minute, the movie's headlong, dance-if-you-dare party vibe never quits.

Like a gambler who won't cash in while he's ahead, "21" just keeps playing, hoping another winning hand will turn up even though its luck's run out.

And that kind of Vegas fantasy always sells -- even if "21" never quite seals the deal.

Contact movie critic Carol Cling at ccling@reviewjournal.com or (702) 383-0272.