This gory prequel is loosely based on the case of the DeFeo murders which took place in the famed house in Ocean Avenue before the Lutz's whose tale was told in THE AMITYVILLE HORROR moved in. When The Montellis an Italian-American family move into the not-yet notorious home it's not long before rebellious teenage son Sonny (JACK MAGNER) takes to seducing his sister (Diane Franklin THE LAST AMERICAN VIRGIN BETTER OFF DEAD) and slaughtering the entire family. Investigation by the authorities points to the boy's demonic possession which is later evidenced by a grisly EXORCIST-inspired physical transformation. Screenwriter Tommy Lee Wallace is a frequent collaborator of John Carpenter.