U.S. actor Matt Damon poses for a fan taking his picture during "The Informant" premiere at the 66th Venice Film Festival September 7, 2009. [Agencies]

LOS ANGELES- That exclamation point in "The Informant!" is a tipoff to what director Steven Soderbergh and writer Scott Z. Burns have in mind.

Without that punctuation, this tale of corporate skullduggery, embezzlement, wiretaps, a whistle-blower and mental illness would be either a sweaty-palm thriller or a gritty character study about matters of conscience in corporate America. But that exclamation point changes everything. It's a comedy! And Matt Damon is playing a Tom Ripley without any smarts -- or at least without any instinct for self-preservation.

Perhaps the only way to tell the bizarre yet (mostly) true account of Mark Whitacre is as a comedy. It's somewhat akin to Steven Spielberg's "Catch Me If You Can," about a fabulous con artist who fakes out so many people that even he can't sort out truth from fiction. This is tricky stuff: a comedy about things that aren't really funny. With the right tone, you can maybe pull this off, but Soderbergh chooses to throw all subtlety aside.

Marvin Hamlisch's jaunty score, like something out of a 1960s Doris Day movie, and the protagonist's inner monologue, rambling the length of the movie and throwing off extremely weird fragments from a disordered mind, all but beg an audience to laugh. And, here and there, no doubt they will. The Warner Bros. release opens on September 18.

But how many people are going to care terribly about a protagonist, a compulsive liar, who keeps pulling the rug out from under himself? The movie insists that all this is hilarious, but it feels like desperate pleading. Which lies are you supposed to laugh at exactly?

Burns' script is based on the book "Informant" -- notice the lack of an exclamation point -- by Kurt Eichenwald, a former New York Times reporter. It centers on a complex individual, a top executive at agribusiness giant Archer Daniels Midland, who helped the FBI expose price fixing at that company in the 1990s. Eventually, he also was prosecuted for embazzling huge amounts of money.

In the movie, a running monologue by Whitacre makes it clear this is not a normal guy. He obsesses over trivia while ignoring major problems. And he plays a blame game in which his errors in judgment can always be laid off on someone else.

His view of the world is skewered and, yes, at times funny. The youngest divisional president in the company's history, pressure falls heavily on him when a lab problem puts the division into the red. It proves much easier to blame corporate sabotage than to admit failure.That brings the FBI into his world, and soon his wife, Ginger (Melanie Lynskey), demands he tell the agents about the crimes ADM forces him to commit. And soon, his FBI handlers, agents Shepard (Scott Bakula) and Herndon (Joel McHale), are asking him to "wear a wire." Just like in the movies.

Suddenly, the mousy corporate suit sees himself in a white hat. He's a spy! He calls himself agent 0014 since he's "twice as smart as 007."

Soderbergh's whimsical direction conditions a viewer not to trust this protagonist. So you feel no surprise that the sabotage allegation proves false. Then again, some wild tales prove to be true: The ADM vice chair (Tom Papa) and other suits do get into surreptitiously recorded conversations with foreign competitors about price fixing. Whitacre only has to coach them a little bit to say the right words. Then the fictional house of cards slowly tumbles around the FBI, bewildered DOJ lawyers and his own attorneys. Each lie leads to a more elaborate lie. The movie hints that much of this erratic behavior is explained by a bipolar disorder, but there is never a clear diagnosis.

Damon's master liar is no smooth customer. You can sense the sweat on his lips. His answers come too fast, and his hands and feet are in constant motion. It's a body trying to keep up with an overactive mind. Everyone else in the movie mostly reacts in bewilderment. Except for Lynskey's Ginger, the one calm person amid chaos. Is she on to her husband or is she clueless? That answer never comes. Soderbergh, acting as his own cinematographer under the name Peter Andrews, is in love with the HD digital camera Red Cam, so light levels are low and natural. Which is somewhat at odds with the comic mode of the film. But then again, the whole film, a comedy about crime and mental illness, seems at war with itself.