The exclamation point in the title is your first clue that Steven Soderbergh's intentions are more than a little askew with "The Informant!"

Then you notice Matt Damon's helmet of hair, his pouf of a moustache, his corny sportswear and the paunch where the "Bourne" trilogy star's taut abs used to be. And once the strains of Marvin Hamlisch's jaunty score begin - an ideal accompaniment to the faded, '70s-style cinematography - you know you're in some vividly retro, comic parallel universe.

"The Informant!" is about a serious, real-life subject - a whistle-blower who spied for the FBI to expose corporate corruption - only Soderbergh, directing a script by Scott Z. Burns, approaches it in the goofiest way, rather than as a serious drama like "The Insider" or even his own "Erin Brockovich."

It's a kick, really, but it also keeps you guessing: Is Damon, as Mark Whitacre, just a regular guy who gets in over his head? Is he far more scheming and malevolent than his folksy Midwestern demeanour would suggest? Or is something else entirely going on here?

Damon doesn't just dig into the role physically. He also keeps you on your toes with Whitacre's happy-go-lucky personality, a misplaced confidence that buoys him regardless of the situation, coupled with a surprisingly high comfort level for duplicity. It's a welcome opportunity to watch him show off his comedic abilities; come to think of it, Soderbergh, with his "Ocean's" movies, is one of the few directors who give him that chance.

One of the neatest tricks that throws us off course is Whitacre's running interior monologue: a series of voiceovers in which he provides stream-of-consciousness musings on everything from indoor pools to Brioni ties to the Japanese word for tuna. His thoughts may not be as innocuous as they seem.

Based on the book by former New York Times writer Kurt Eichenwald, "The Informant!" follows Whitacre's misadventures as he agrees to wear a wire to expose a price-fixing scheme at Archer Daniels Midland, the Illinois-based agribusiness conglomerate where he's an executive. Actually, "agrees" doesn't even begin to describe his reaction. He's more like a giddy little boy playing Agent 007 - or 0014, as he describes himself, because he thinks he's twice as smart.

He's totally convinced himself that he's on a mission, that he's doing the right thing for the greater good. At the same time, he tries to maintain the facade of living an idyllic, upper-middle class life with his perfectly coiffed wife, Ginger (Melanie Lynskey), who always serves a proper dinner in the dining room for Whitacre and their children.

But as his ineptitude evolves into unreliability and eventually desperation, he becomes more trouble than help to agents Brian Shepard (Scott Bakula) and Bob Herndon (Joel McHale). The deeper Whitacre gets, the more damage he does to the investigation - all of which Soderbergh plays for deadpan laughs, which makes it all the more absurd.

One question lingers, though: What does his wife know and when does she know it? Ginger is the weak link here, her docile, doting presence making us wonder whether she's aware of her husband's true nature, having been with him since childhood.

Some insight would have been helpful, could have fleshed things out. But the joke might just be on her, as it is on us.