Heather Graham and Justin Bartha have signed on to join the cast of Warner Bros. and Legendary Pictures' Hangover, directed by Todd Phillips.

According to The Hollywood Reporter, the story revolves around three buddies, played by Bradley Cooper, Ed Helms and Zach Galifianakis, who lose their best friend (Bartha) at his Caesars Palace bachelor party just 40 hours before his wedding. The trio must attempt to retrace all their bad decisions from the night before and figure out where things went wrong.

The movie begins production this week in Las Vegas.

The Hangover was released June 5th, 2009 and stars Bradley Cooper, Ed Helms, Zach Galifianakis, Justin Bartha, Heather Graham, Sasha Barrese, Jeffrey Tambor, Ken Jeong. The film is directed by Todd Phillips.