Doug (Justin Bartha) is about to be married, so his friends -- Stu (Ed Helms), a dentist planning on proposing to his girlfriend of three years, Phil (Bradley Cooper), a schoolteacher bored of the married life, and Doug's soon to be brother-in-law Alan (Zach Galifianakis), who is smart yet socially-inept -- take him to Las Vegas for a bachelor party. Stu's girlfriend is very controlling, thereby forcing Stu to lie to her about their destination.