The story revolves around Peter Bretter, who is a music composer for a TV show that happens to feature his girlfriend, Sarah Marshall, in the lead role. After a five-year relationship, Sarah abruptly breaks up with Peter. Devastated by this event, he chooses to go on a vacation in Hawaii, in order to try to move forward with his life. Trouble ensues when he runs into his ex on the island as she is vacationing with her new boyfriend.