The Informant!

Matt Damon reportedly gained 30 pounds to prepare for his role as whistleblower Marc Whitacre in Steven Soderbergh's THE INFORMANT! , based on a true story.  Damon doesn't look like he's wearing a fat suit, but he's certainly not playing Matt Damon. He's terrific in this role, taking it over and convincing us to believe just about anything he says and does.

It's 1992, and Whitacre is a young executive at Archer Daniels Midland.  In the heartland plant where he works as a chemist, a virus is attacking a new food additive.  He eventually agrees to the FBI's request that he wear a wire in order to find out what's gone wrong.  

Without giving too much away, it's safe to say that the plot doesn't unravel as much as it gets more and more focussed.  You think you know what's going on, and then you realize that you don't, and then you think you've finally got it straight.  It's a movie to see with friends, maybe more than once, so that you can compare clues.

Watch for small roles featuring standup comics, such as the Smothers Brothers as judicial figures.