Lt. Duvalier (Jack Nicholson), a French soldier, loses contact with his unit and is forced to wander alone near the Baltic Sea. While in search of his regiment, he spies Helene (Sandra Knight), a mysterious beauty, walking by herself. Mesmerized, Duvalier begins tracking her, but she vanishes. He later catches up with her and follows her into a castle, where he encounters the bizarre Baron Von Leppe (Boris Karloff), finds signs of witchcraft, and learns the shocking truth about Helene.