It's 2004 and retired military MP Hank Deerfield (TOMMY LEE JONES) receives a phone call that his son, Mike (JONATHAN TUCKER), has gone AWOL from Fort Rudd while on leave from the Iraq War. Leaving his wife, Joan (SUSAN SARANDON), at home, Hank drives to New Mexico, determined to find his boy and return him to his unit before he gets into any more trouble.
With limited assistance from Lt. Kirklander (JASON PATRIC), Hank tries to find any sort of clue that might help him, and he finds that in his son's cell phone. Yet, the video on it taken in Iraq is mostly garbled, so while a local technician tries to salvage what he can and send it to Hank piecemeal, the former military man keeps digging.
He runs into resistance, though, from local cop Det. Emily Sanders (CHARLIZE THERON) who has her own issues in the form of constantly being belittled by her male comrades simply due to her gender, something her superior, Chief Buchwald (JOSH BROLIN) doesn't realize or simply overlooks.
With no missing person authority since this is a military matter, she tells Hank she can't help. That is, until a body is found in disputed civilian vs. military jurisdiction. Identified as Mike, that discovery creates an unlikely partnership between Hank and Emily.
As they interview those in Mike's platoon -- Specialist Ennis Long (MEHCAD BROOKS), Specialist Gordon Bonner (JAKE MCLAUGHLIN), Corporal Steve Penning (WES CHATHAM) and Private Robert Ortiez (VICTOR WOLF) -- they must overcome various obstacles as they try to find out what happened to the young soldier and why.