Two days before his wedding, Doug, his three friends, and sister Sophie drive to Las Vegas for a wild and memorable stag party. In fact, when the three groomsmen and bridesmaid wake up the next morning, they can't remember a thing; nor can they find Doug. With little time to spare, the four hazy pals try to re-trace their steps and find Doug. During this time feelings arise with Phil and Sophie, but they must focus and find Doug so they can get him back to Los Angeles in time to walk down the aisle. following hangover 2 and 3 also*