Grief-stricken over his partner Sydney's death, Gavin sets fire to every reminder in the couple's home before fleeing Los Angeles for New Jersey, where he hopes to find peace with the family of an old friend. Instead, he finds Joan. Joan, the family's ten-year-old daughter, was born Highly Superior Autobiographical Memory, or HSAM: the rare ability to recall every day of her life in cinematic detail. Joan has never met Gavin until now, but she did know his partner, and waiting inside her uncanny mind are startlingly vivid memories to prove it. Gavin strikes a deal with Joan: in return for sharing her memories of Sydney, Gavin will help her win a songwriting contest she's convinced will make her unforgettable. The unlikely duo set off on their quest until Joan reveals unexpected details about Sydney's final months, forcing Gavin to question not only the purity of his past with Sydney but the course of his own immediate future.