Chauffeur Bruno (Lon Chaney Jr.) looks after three strange siblings at their family estate. Ralph (Sid Haig), Virginia (Jill Banner) and Elizabeth (Beverly Washburn) all suffer from an inherited condition: a genetic disorder that causes a reversal in mental age and results in a crazed, childlike disposition. Because of his affection for the family, Bruno covers up the siblings' bizarre behavior and crimes. But, when relatives arrive at the family estate, the truth is bound to come out.