The Hangover follows a group of friends who head to Las Vegas for a bachelor party. With Doug (Justin Bartha) preparing for his wedding, his friends Phil, (Bradley Cooper), Stu (Ed Helms), and Alan (Zach Galifianakis) take him on a night he'll never forget, After blacking out, the group - who call themselves the "Wolf Pack" - realize that they've lost Doug, and must retrace the steps of the most outrageous night of their lives in order to find him.