Two days before his wedding, Doug (Justin Bartha) and three friends (Bradley Cooper, Ed Helms, Zach Galifianakis) drive to Las Vegas for a wild and memorable stag party. In fact, when the three groomsmen wake up the next morning, they can't remember a thing; nor can they find Doug. With little time to spare, the three hazy pals try to re-trace their steps and find Doug so they can get him back to Los Angeles in time to walk down the aisle.