Dr. Roger Girard (Bruce Dern) is a rich scientist experimenting with head transplantation. His caretaker has a son, Danny (John Bloom), who is an extremely strong full-grown man, but he has the mind of a child. In an unusual turn of events, Manuel Cass (Albert Cole), a maniacal killer, has murdered Dr. Griard's caretaker and is badly injured himself. Dr. Girard decides to transplant the murderer's head onto Danny's body. The new creature, with one head of a murderer and the other with the mental capacity of an eight-year old attached to an extremely powerful body, begins wreaking havoc.