1960s black comedy horror starring Lon Chaney Jr. Chauffeur Bruno (Chaney Jr.) watches over Virginia (Jill Banner), Ralph (Sid Haig) and Elizabeth (Beverly Washburn), the three inbred, grown-up children of the Merrye family who have inherited a genetic condition which turns them into demented, feral beings. While Peter (Quinn Redeker) and Emily (Carol Ohmart), who have come to claim the Merrye mansion as their own, are visiting, Bruno has to leave the house for a short time. The siblings take the opportunity to wreak havoc and when Bruno returns he realises he must go to drastic measures to stop the 'Merrye Syndrome' from spreading.