<P> Peter begins spending time with Rachel and starts to develop feelings for her . 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 that Aldous is about to embark on a world tour with his group, Infant Sorrow, for 18 months . 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, while Peter (through observing Sarah's relationship with Aldous) begins to realize that his relationship with her wasn't as great as he remembered . </P> <P> Sarah, Aldous, Peter, and Rachel later share an awkward dinner together . After the dinner, Peter takes Rachel back to his hotel room and they begin to have sex . 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 competition and become even louder . When Aldous realizes Sarah is clearly putting on a performance to provoke a reaction from Peter, he stops the sex and tells her the trip was a mistake as she's clearly not over Peter . They bicker furiously, 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 takes down a naked picture of Rachel from a local bar despite enduring a beat - down from the owner . </P> <P> He flies back to Los Angeles and after a period of sadness and self - loathing, he begins working on his Dracula puppet comedy - 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 . </P> <Ul> <Li> Jason Segel as Peter Bretter: A slobbish but well - meaning composer for the TV show Crime Scene: Scene of the Crime . On the side, he is working on a Dracula - based rock opera involving puppets called A Taste for Love in which he performs as Count Dracula . </Li> <Li> Kristen Bell as Sarah Marshall: A famous working actress for the TV show Crime Scene: Scene of the Crime who dated Peter before leaving him for rock star Aldous Snow . </Li> <Li> Mila Kunis as Rachel Jansen: A receptionist for the Hawaiian resort Turtle Bay with whom Peter forms a relationship during his stay at the hotel . </Li> <Li> Russell Brand as Aldous Snow: Sarah Marshall's rock star boyfriend . The same character is later seen in Get Him to the Greek . </Li> <Li> Bill Hader as Brian Bretter: Peter's stepbrother and best friend who usually criticizes him for the better . He helped out in his stepbrother's A Taste for Love opera where he performed Van Helsing . </Li> <Li> Jonah Hill as Matthew Van Der Wyk: A waiter at Turtle Bay and obsessive fan of Aldous . </Li> <Li> Liz Cackowski as Liz Bretter: Brian's wife who was his one and only girlfriend and who usually sneaks in on Brian's computer conversations . </Li> <Li> Da'Vone McDonald as Dwayne: A bartender at Turtle Bay . Dwayne was originally from South - Central Los Angeles, and hated it there, until he moved to Oahu, where he learned to name over two hundred different kinds of fish . </Li> <Li> Jack McBrayer as Darald Braden: A guest at the resort who does not like certain aspects of sexual intercourse and is having trouble satisfying his new wife . </Li> <Li> Maria Thayer as Wyoma Braden: The sex - hungry wife of Darald . </Li> <Li> Paul Rudd as Chuck / Kunu: An air - headed surfing instructor who is 44 years of age by his own estimate . </Li> <Li> Jason Bateman as Animal Instincts Detective: A character on Sarah Marshall's latest show, Animal Instincts . </Li> <Li> William Baldwin as Himself / Det . Hunter Rush: In the film's universe, Baldwin is the "hard - to - love" co-star on Sarah's show . He is referred to as "Billy Baldwin" and Peter briefly suspects him of having an affair with Sarah . </Li> <Li> Teila Tuli as Kimo: A cook at Turtle Bay . </Li> <Li> Branscombe Richmond as Keoki: The bartender who beats up Peter when he takes down Rachel's picture from the bar . </Li> <Li> Kristen Wiig (unrated version) as Prana: A yoga instructor . </Li> </Ul>

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