Struggling musician Peter Bretter has spent six years idolizing his girlfriend, television star Sarah Marshall. He's the guy left holding her purse in paparazzi photos and accidently omitted from acceptance award speeches. But his world is rocked when she dumps him and Peter finds himself alone. After an unsuccessful bout of womanizing and an on-the-job nervous breakdown, he sees that not having Sarah may just ruin his life.
To clear his head, Peter takes an impulsive trip to Oahu, where he is confronted by his worst nightmare: his ex and her tragically hip new British-rocker boyfriend, Aldous, are sharing his hotel!
When he gets suddenly and unceremoniously dumped by his longtime girlfriend, television star Sarah Marshall, composer Peter Bretter is devastated. Miserably depressed, he seeks solace in tawdry one-night stands, but he is desperate to win Sarah back. On the advice of his stepbrother, Brian, Peter heads off to Hawaii for a much-needed vacation, but he gets even more freaked out when he discovers that Sarah and her new beau, wild and wacky British singing sensation Aldous Snow, are staying there as well.