Having thought that monogamy was never possible, a commitment-phobic career woman may have to face her fears when she meets a good guy.

Composer Peter Bretter (Jason Segel) is in a five-year relationship with actress Sarah Marshall (Kristen Bell), who stars in a ''CSI: Crime Scene Investigation''-like television show titled ''Crime Scene: Scene of the Crime''. One day, as Peter stands stark naked in their apartment, Sarah announces that she is breaking up with him. Devastated, and unable to banish his grief through one-night stands, Peter takes a trip to Hawaii. However, the vacation is ruined when he learns that Sarah and her new rock star boyfriend Aldous Snow (Russell Brand) are also guests of the resort. Taking pity on him, hotel concierge Rachel (Mila Kunis) offers him an expensive suite for free in exchange for cleaning up the room himself.