The Hollywood Reporter reports that Heather Graham and Justin Bartha ("National Treasure") will join the cast of "The Hangover" for Warner Bros. and Legendary Pictures. Shooting begins this week in Las Vegas.

The movie tells of three best friends - played by radley Cooper, Ed Helms and Zach Galifianakis - who lose their friend (Bartha) at the Caesars Palace during a bachelor party just 40 hours before the wedding. The trio must attempt to retrace all their bad decisions from the night before and figure out where things went wrong. Graham will play a Vegas local who crosses paths with the guys and might know more about the groom than she lets on.