British pirate William Kidd (Charles Laughton) captures Adm. Blayne's (Randolph Scott) treasure ship and hides the bounty in a cave. Three years later, Kidd, posing as a sea captain, offers his services to the king as an escort ship. Seeking a social position, Kidd also negotiates for Blayne's title and lands, if he can prove Blayne was associated with piracy. On his mission, Kidd is unaware that Blayne's son, Adam (also Scott), is among the crew, determined to clear his father's name.