Two days before his wedding, Doug (Justin Bartha) and his three buddies (Bradley Cooper, Ed Helms and Zach Galifianakis) drive to Vegas for blow-out night they'll never forget. But when the three groomsmen wake up the next morning with pounding headaches, they can't remember a thing. Their posh hotel suite is beyond trashed and the groom is nohere to be found.
With no clue of what happened and little time to spare, the trio must attempt to retrace their bad decisions from the night before in order to figure out where things went wrong and hopefully get Doug back to L.A. in time wedding.
However, the more they begin to uncover, the more they realize just how much trouble they are really in.