After discovering she's inherited a remote island in Canada from the estranged grandfather she was never allowed to meet, 17-year-old Annie Jacobson decides to investigate, pulling her into a world of buried secrets, unexpected sisterhood, and the complicated family history she was never meant to find.

An 18th birthday mushroom trip brings free-spirited Elliott face-to-face with her wisecracking 39-year-old self. But when Elliott’s "old ass" starts handing out warnings about what her younger self should and shouldn't do, Elliott realizes she has to rethink everything about family, love, and what's becoming a transformative summer.