During a seaside holiday on the Baltic coast, 40-year-old Miriam (Martina Gedeck) arrives with her long-time partner, André, her 15-year-old son, Nils, and Nils's 12-year-old girlfriend, Livia. Miriam becomes increasingly alarmed when Livia begins spending time with Bill (Robert Seeliger), a charismatic 38-year-old American sailor. Initially stepping in out of maternal concern over Bill's inappropriate interest in the underage girl, Miriam's protective instinct turns into jealousy when she finds herself strongly attracted to Bill as well. She initiates a secret affair with him behind her partner's back, setting off a chain of moral complications and tragic consequences for the entire group.