Henry Roth is a veterinarian at Sea Life Park on Oahu. His closest friends are Ula, a marijuana-smoking Islander; Alexa, his androgynous assistant; Willy, his pet African penguin; and Jocko, a walrus.

Henry's boat breaks down, so he goes to the Hukilau Café to wait for the Coast Guard. He sees Lucy Whitmore make architectural art with her waffles. Henry assumes she is a local, which prevents him from introducing himself, but the next day he comes back and has breakfast with her. Lucy asks to see him again the next morning.

The next day, Lucy shows no recollection of ever meeting him. The restaurant owner Sue explains to Henry that the year before, Lucy and her father Marlin went up to the North Shore to pick a pineapple for his birthday. On the way back, a car accident left Lucy with anterograde amnesia. To save her the heartbreak of reliving the accident, Marlin and Doug, Lucy's lisping steroid-addicted brother, re-enact Marlin's birthday.

Despite Sue's warning, Henry tries to get Lucy to have breakfast with him again. It ends poorly when Henry unintentionally hurts Lucy's feelings. At her house, Marlin and Doug instruct Henry to leave Lucy alone. Henry begins concocting ways to run into Lucy through the following days, during which he manages to successfully impress her over a series of "first" dates and "chance" encounters. Later, Marlin and Doug give their permission for Henry to continue when they discover Lucy regularly singing the Beach Boys' "Wouldn't It Be Nice" in her painting studio – the first major change in her routine since the accident.

One day, as Henry is about to sit with Lucy at breakfast, she notices a police officer writing a ticket because of her expired plates. With the ruse exposed, Lucy is distressed to learn that her friends and family have maintained the charade for so long; however, in watching her reaction, Henry surmises that her strongest reactions are to feeling betrayed by her loved ones, not the actual memory loss.

Henry devises a new strategy to let Lucy know about the truth by creating a video with her friends to explain the situation calmly; rather than let her go through her pre-accident routine, they plant the video in her room with a note to play it when she first wakes up. The strategy works and allows Lucy to process the events while catching her up on current events, including her relationship to Henry. Henry and Lucy's relationship grows well using this method, and they continue to refine the process while enduring some humorous setbacks such as their sleeping together and Lucy attacking Henry the next morning. However, when Lucy discovers that Henry has decided to cancel ten years' worth of planning for his research study of walruses in Bristol Bay to help manage her condition, she decides that they need to break up. Henry reluctantly helps her destroy her journal entries of their relationship and effectively "erase" their time together.