A man with brutal and macabre origins, Leon Corledo (Oliver Reed) was raised in the home of Don Alfredo Corledo (Clifford Evans), his kind and loving adopted father. When he leaves Don Alfredo to find work, Leon discovers that he has increasingly violent urges. Although these tendencies are calmed by Leon's love for the beautiful Christina (Catherine Feller), he ultimately cannot contain his curse and transforms into a werewolf, terrorizing the Spanish countryside.