Composer Peter Bretter finds himself shattered when his girlfriend of five years, Sarah Marshall—a promising TV actress—unexpectedly ends their relationship. In an attempt to heal from his heartbreak, he decides to escape to Oahu for a much-needed vacation. Unfortunately, his plans for a peaceful retreat are shattered when he discovers that Sarah is staying at the same resort with her new boyfriend, the charming British rock star Aldous Snow. Fortunately for Peter, a compassionate hotel concierge named Rachel Jansen takes pity on him and generously offers him an opulent suite at no charge.
Peter's sorrow deepens as he awkwardly encounters Sarah and Aldous repeatedly, all while surrounded by blissful couples enjoying their getaways. However, the mood shifts when he starts to bond with Rachel, gradually igniting romantic feelings for her. One evening, while enjoying each other's company, Peter opens up to Rachel about his dissatisfaction with his mundane job composing music for TV shows, admitting that his heart truly lies in creating a Dracula puppet comedy-rock opera. Encouragingly, Rachel challenges him to perform a song from his opera at a local bar, spurring him on as he delivers an enthusiastic rendition.
During a hiking excursion with Rachel, she dares Peter to leap off a cliff into the ocean. He takes the plunge but finds himself precariously hanging from some vines. With a gentle push from Rachel, he lets go and splashes safely into the water, culminating in a kiss that signals a budding connection. Meanwhile, turmoil brews in Sarah and Aldous's relationship, particularly after the cancellation of Sarah's latest TV show and the revelation that Aldous will soon embark on an 18-month world tour with his band, Infant Sorrow. To make matters worse for Peter, he is moved to a suite directly next to Sarah's.
The tension escalates when Peter runs into Aldous while surfing. Aldous abruptly informs Peter that he and Sarah had started their affair a whole year before their breakup. Confronted by this revelation, Peter later approaches Sarah, who candidly expresses her feelings of emotional detachment from him, claiming their relationship was beyond salvaging.
As the romance between Peter and Rachel blossoms, jealousy stirs within Sarah. The four—Peter, Rachel, Sarah, and Aldous—share a hilariously uncomfortable and drunken dinner that ends with Peter and Rachel retreating to his hotel room, where they begin to make love. Unbeknownst to them, Sarah tries to provoke a reaction by initiating intimacy with Aldous, leading to a heated argument that culminates in Aldous ending their relationship.
After learning that Aldous has split with Sarah, Peter visits her to provide comfort, leading to Sarah's unexpected confession of love and a desire to rekindle their romance. Caught off guard, Peter suddenly halts their moment, realizing his heart belongs to Rachel instead. In a bid to mend things with Rachel, he seeks her out for forgiveness, but she, filled with hurt, orders him to leave her forever. Before departing, Peter makes a stop at a bar to return a topless photo of Rachel that had been displayed without her permission, only to end up battered by the bar owner in the process.
Returning to Los Angeles, Peter spirals into a phase of sadness and self-recrimination. However, he channels his pain into creating his Dracula puppet opera, A Taste for Love, and extends an invitation to Rachel for the performance. Initially hesitant, Rachel ultimately decides to attend, and after a triumphant show, she finds Peter to congratulate him and reveals she might consider staying nearby. As she makes an exit to let him relish in his success, she swiftly returns to his dressing room, expressing how much she misses him, leading to a heartfelt embrace and kiss that closes their story on a hopeful note.
