In a future San Francisco transformed by years of rain, Bo, a 40-year-old lapsed artist, is grieving the community she's lost to catastrophic flooding. Her friends and family have disappeared or fled, the streets are rivers, and the buildings are falling apart. Yet on the day of her planned departure, Bo finds a note slipped under her door: I need help, it reads. Three days a week, afternoons. Can pay in cash. Unable to bring herself to board the ship that could save her life, Bo instead chooses to answer the note, which turns out to have been written by her neighbour Mia, a 130-year-old "supercentenarian" long abandoned by her own family.