Part war film, part political-conspiracy thriller, director Paul Greengrass' "Green Zone" is a fictional account of what would happen if the United States fabricated evidence showing there were weapons of mass destruction in Iraq.

Whether that's deemed preposterous or not likely won't be debated until the end of the movie. That's because during this breathless, fast-paced action piece audiences will be too busy getting their senses assaulted to mind.

It may not be quite as tight and ferocious as Greengrass' other thrillers -- the last two Jason Bourne films -- but "Green Zone" is still a dazzling display of action filmmaking that will keep you caught up for two hours.

Matt Damon returns as Greengrass' star-du-jour, this time he's Chief Warrant Officer Miller, a U.S. Army soldier responsible for uncovering WMDs in Iraq near the end of the invasion-phase of the war.

But Miller's searches come up empty time after time, leading him to believe that something's afoot in military intelligence, especially when a Pentagon official (Greg Kinnear) keeps running interference.

With the help of a local as a translator, Miller uncovers a possible conspiracy about the source of the intelligence and begins his own investigation with the help of CIA operative (Brendan Gleeson) and Wall Street Journal reporter (Amy Ryan).

The film credits as inspiration Washington Post reporter Rajiv Chandrasekaran's Imperial Life in the Emerald City: Inside Iraq's Green Zone. Yet the movie's thesis will make you ponder how the justification for war could be based on such failed intelligence. It also makes a valid point about whether Americans have the right to make decisions that determine Iraq's future.

But all of that really is more of an excuse to fuel the movie from action scene to action scene. Using Greengrass' well-known handheld camera style (the director used the same cinematographer, Barry Ackroyd, who shot "The Hurt Locker," for his brilliant "United 93"), "Green Zone" has the forward narrative thrust of a bullet as Miller races from one incident to another to try and uncover the truth.

The only misstep in the action is the end, with a dark and blurry firefight/chase sequence, that prevents audiences from pinning down the geography of the scene as well as who's shooting who. (Warning to audiences: That "shaky-cam" style on the big screen also is likely to lead to nausea like it did for some in the last two "Bourne" films. My suggestion is to sit several rows more from the screen than you usually do to help avoid motion sickness).

With nods to political thrillers like "JFK" and "The Hunt for Red October," "Green Zone" is a plausible and exhilarating "what-if" scenario for conspiracy theorists and adrenaline junkies alike.