Bourne collaborators Matt Damon and Paul Greengrass may have left the international spy franchise behind after two acclaimed installments, but they fall back on a few of their frenzied storytelling tactics to immerse audiences in The Green Zone, a lock-step military thriller set in Baghdad during the early days of the Iraqi conflict.  Specifically, Greengrass and his Green Zone scripter, Brian Helgeland, rehash the American government's desperate search for the infamous weapons of mass destruction -- or WMDs -- to legitimize our military's Middle Eastern invasion. At the forefront of the ongoing, unorganized investigation is Army Captain Ron Miller (Damon), a dedicated soldier who routinely comes up empty in these treacherous Iraqi sites because vetted intelligence handed to him by his superiors (personified by Greg Kinnear and Brendan Gleeson) proves faulty.  Never one to distance himself from the action, Greengrass trails right behind the stoic Damon and his heroic team as they conduct a wild goose chase around a lit powder keg of political tension and cultural hostility. Green Zone generates immediate urgency by jumping headfirst into the fray, and the director's trademark imagery and in-your-face visuals intentionally keep us off guard. Greengrass knows how to convey the chaos that's erupting around his players, and he presents it to us as if we are a part of the scene, not innocent bystanders tucked safely away in an isolated theater.  But it's not all shock and awe. Helgeland ensures there's heft to this story as well. Sick of the lies being fed to him, Miller goes off the grid and snatches at thin snippets of his own intelligence. By doing so, he almost catches a high-ranking Iraq general, but meets fierce opposition from within the U.S. ranks. Helgeland's screenplay absorbs a number of interesting mysteries and almost ties them together before putting all of its eggs into one finger-pointing basket linked back to power struggles in our own government.    The Greengrass-Damon collaboration is fruitful, though, and they each receive excellent support from the cast and crew. Kinnear seems unusually comfortable playing a manipulative paper pusher, though making him the sole face of the American invasion just so Damon has someone to lecture is a short-sighted mistake that derails the film's final act. Gleeson and Amy Ryan, as a reporter furthering the WMD myth, make the most of their scenes but mostly lob softballs for movie-star Matt to knock out of the park. The film's real revelation is Khalid Abdalla as "Freddy," a local who approaches Damon's character with valuable information, then finds himself part of the hunt.  Green Zone represents the closest we've come to a mainstream Iraq film. It might even benefit from The Hurt Locker's recent Best Picture win, which should blaze a somewhat brighter trail to the multiplexes for audiences who up to this point have proven hesitant.  But Green Zone falters when it strives to be more than just a solid action thriller with semi-contemporary political undertones. Its primary message -- that the U.S. government lied about WMDs to launch an unpopular war -- lost its impact once George W. Bush left office. And the tone of Green Zone goes back even further than 2003, when WMDs dominated national headlines. It also calls to mind 1983, when a lone hero -- usually Sylvester Stallone or Arnold Schwarzenegger -- could singlehandedly decide the outcome of an international conflict simply by choosing to do what was right.