Plot

Devastated Peter takes a Hawaiian vacation in order to deal with the recent break-up with his TV star girlfriend, Sarah. Little does he know, Sarah's traveling to the same resort as her ex - and she's bringing along her new boyfriend.

Peter is a composer and a likable sad sack who's devastated when his girlfriend of five years, Sarah Marshall, the star of a cheesy CSI-style crime show, dumps him. He weeps, he rails, he mopes. Finally, his step-brother Brian suggests a vacation, so Peter heads for a resort on Oahu where, as he's checking in, he sees Sarah and her new beau, Aldous, a perverse English rocker. The weeping and moping start again, until Peter is rescued by Rachel, a thoughtful hotel clerk who invites him to a luau and to hang out. Although he constantly runs into Sarah and Aldous, Peter starts to come alive again. Will Sarah realize what she's lost, and what about Rachel?—<jhailey@hotmail.com>

Composer and musician Peter Bretter, unmotivated in life, is unceremoniously dumped by his girlfriend of five and half years, Sarah Marshall, the star of the hit television show, Crime Scene. Peter is devastated as he is in love with Sarah, who has left him for another undisclosed man. The situation is made all the more difficult for Peter as he also works on Crime Scene. Peter's stepbrother, Brian Bretter, trying to be his voice of reason, tells Peter among other things to go away on vacation to forget about Sarah. The place Peter chooses is the Turtle Bay Resort in Hawaii, a place where Sarah had mentioned wanting to go. So it is not totally coincidental that upon Peter's arrival, he finds that Sarah is also there with her new boyfriend Aldous Snow, the pretentious lead singer for the band Infant Sorrow. Peter's plan of forgetting about Sarah is impossible, of which the staff and many of the guests at the hotel are aware, but neither Peter or Sarah refuse to let the other's presence at the resort make them run away. With the help of Brian, Brian's wife Liz and the hotel staff, Peter tries to move on with his life specifically with Rachel Jansen, one of the customer service agents at the hotel, who is carrying some emotional baggage of her own. But Peter goes into a further emotional tailspin when Sarah's life also takes a turn.—Huggo

When Sarah Marshall dumps aspiring musician Peter Bretter for rock star Aldous Snow, Peter's world comes crashing down. His best friend suggests that Peter should get away from everything and to fly off to Hawaii to escape all his problems. After arriving in Hawaii and meeting the beautiful Rachel Jansen, Peter is shocked to see not only Aldous Snow in Hawaii, but also Sarah Marshall.—FilmFanUk

Composer Peter Bretter (Jason Segel) is in a five-year relationship with actress Sarah Marshall (Kristen Bell), who stars in a CSI-like television show, "Crime Scene: Scene of the Crime." Sarah is hot and her career is on the rise, while Peter is a sloth and spends most of his time at home, hoping for inspiration to strike. Sarah believes that Peter is holding her back.

One day, as Peter stands stark naked in their apartment, Sarah announces that she is breaking up with him. Sarah says that she loves someone else. Peter goes through a period of isolation and meets his stepbrother Brian (Bill Hader) who tells him to get on with his life and complete the Dracula musical that he has been working on. Brian agrees to be Peter's wing-man as he goes to nightclubs to pick girls.

Still Peter is devastated, and unable to banish his grief through one-night stands. Brian visits Peter at home, which is now filthy and disgusting, and Peter is despondent that everything in his home reminds him of Sarah and that he is still in love with her. Brian advises Peter to go for a vacation.

Peter takes a trip to Hawaii as this was also the destination that Sarah had suggested when they were together. However, the vacation is ruined when he learns that Sarah and her new boyfriend Aldous Snow (Russell Brand), lead singer of the English rock band Infant Sorrow, are also guests of the resort. Aldous is a ladies' man, and a complete player and Peter knows Sarah and Aldous are having a sex romp at the resort. Aldous and Sarah have an awkward introduction with Peter at the reception, witnessed by the concierge. Peter had showed up without a reservation and was told that the only suite available was $6000 / night.

Taking pity on him, hotel concierge Rachel (Mila Kunis) offers him the expensive suite for free for 4 nights in exchange for cleaning up the room himself.

Peter's heartbreak is aggravated by awkward run-ins with Sarah and Aldous, along with seeing all the vacationing couples at the resort. Peter believes that he is ruining Sarah's vacation by being in her face, but she has rigorous sex with Aldous regardless, in many different positions and at all times of the day. Sarah suspects that Peter followed her to Hawaii by talking to her assistant, but Peter assures her that he was there on his own and meeting her was just a coincidence.

Peter begins spending time with Rachel and starts to develop feelings for her. While hanging out one night, Peter confesses to Rachel that he hates his day job composing TV show music and that his true passion is writing a Dracula puppet comedy-rock opera. At a bar, Rachel volunteers Peter to sing a song from the opera and cheers him on as he performs the number.

On a day out hiking with Peter, Rachel dares him to jump off a cliff into the ocean. He makes the jump but is caught by some vines and is left dangling off the edge. With some prodding from Rachel, he lets go and safely lands in the water, after which she kisses him.

Meanwhile, the relationship between Sarah and Aldous begins to falter. Much of the discord is triggered by the news that Sarah's TV show has been canceled, and Aldous is about to embark on a World Tour with his group for 18 months. At the same time, Peter's room is needed by new occupants, and he is placed in the suite next door to Sarah's.

During a day of surf and sand Aldous and Peter run into each other and begin talking. Inadvertently, Aldous informs Peter that he and Sarah began having sex a full year before she broke up with Peter. When Peter confronts Sarah, she tells him she began feeling disconnected emotionally from him and she couldn't do anything to make their relationship work. Further exacerbating the situation is Sarah's obvious jealousy of the budding relationship between Peter and Rachel.

Later, Sarah, Aldous, Peter and Rachel share an awkward dinner together. After the dinner, Peter takes Rachel back to his hotel room and they begin to fool around. Sarah hears them through the wall and initiates sex with Aldous, moaning loudly for the benefit of the couple next door, and Rachel and Peter turn the situation into a game and become even louder. When Aldous realizes Sarah is clearly putting on a performance to try and get a rise out of Peter, he stops the sex and tells her the trip was a mistake as she's clearly not over Peter. They bicker furiously and cruelly, prompting Aldous to announce that the relationship is over.

The next day Peter encounters Aldous and learns that he and Sarah have broken up and that he is flying back to England. Peter goes to Sarah's room to console her where she admits she still loves him and tries to rekindle their romance. The two start to engage in sexual activity, but Peter abruptly cuts it off because of his feelings for Rachel, and his now ambivalent feelings towards Sarah.

Peter immediately goes to Rachel to confess what happened, but she is hurt and demands that he leave and never contact her again. Before leaving, Peter goes to the bar they visited and removes a topless photo of her that was hung in the restroom's art collage without her consent. He returns the photo to her, bruised from a beat-down by the bar owner.

He flies back to Los Angeles and after a period of sadness and self-loathing, he begins working on his Dracula puppet rock opera, A Taste for Love. He sends an invitation to Rachel for the opening night performance. Although extremely hesitant at first, Rachel eventually decides to attend. After the performance Rachel congratulates Peter and tells him she's looking into attending school in the area. She leaves so Peter can bask in the success of his show, but quickly returns to Peter's dressing room to tell him she misses him. Peter tells her that he has missed her too. The film ends as they embrace and kiss.