The wicked Alain, Sire de Maletroit (Laughton), plots elaborate revenge against his younger brother Edmund (Cavanagh). Twenty years previously, Alain's lover left him for Edmund and they ran away to marry; she died in childbirth. Alain imprisoned Edmund in the dungeon of the family manor, and convinced his young niece Blanche that her father was dead. When Blanche reaches adulthood, Alain plans to make her life miserable by marrying her off to a well-born cad, Denis de Beaulieu (Wyler). But Denis and Blanche fall in love and try to escape, leading to a deadly confrontation with Alain in his dungeon deathtrap.—balkaster