In the Pacific after the war, a U.S. Marine unit that includes Sgt. Phil O'Hara (Aldo Ray) is awaiting discharge when missionary Alfred Davidson (Jose Ferrer), physician Dr. Robert McPhail (Russell Collins) and singer Sadie Thompson (Rita Hayworth) arrive at the base. The soldiers are delighted by the spirited, friendly Sadie, and Phil falls in love with her. Davidson, however, unearths a secret in Sadie's past and, blocking her attempt to leave the island, demands that she repent.