Composer Peter Bretter (Jason Segel) has spent five years adoring his girlfriend, television star Sarah Marshall (Kristen Bell). He has had success for composing the theme song and score of her highly-rated crime drama show. While writing a puppet musical about Dracula, he's the guy left holding her purse in paparazzi photos and accidentally omitted from acceptance award speeches. Things take a twist when she breaks up with him, and Peter suddenly finds himself alone. Trying to get over her, he has sex with various women, but besides getting an STD scare, all this does is increase his stress and heartache. After an on-the-job nervous breakdown, he sees that not having Sarah may just ruin his life. At the suggestion of his stepbrother Bryan (Bill Hader), Peter takes an impulsive trip to Hawaii to clear his head. At Turtle Bay Resort, he is confronted by his worst nightmare: Sarah and her narcissistic new British-rocker boyfriend, Aldous Snow (Russell Brand), are staying at his hotel. As he torments himself with the reality of Sarah's new life, he finds relief when talking with Rachel (Mila Kunis), a beautiful resort employee whose laid-back approach tempts him to rejoin the world. Although they bond and get along well, she is also reluctant to move on, because she too has been recovering from a recent heartbreak. Throughout the film, a number of quick flashbacks reveal the negative aspects of Sarah and Peter's relationship, which the latter mostly ignored or was completely oblivious to. It is made known that she cheated on him with Aldous for about a year without him knowing, but after they break up, she now realizes that she wants him back. In the end, Peter is willing to take her back, but at the last minute, he turns her down upon realizing she is not worth it if she did not really love him. He settles down with Rachel, now finally having moved on with his life.