It is the swinging 60s in London's Carnaby Street and a group of bored teenagers including Chris (Frankie Avalon), Sheila (Jill Haworth), Gary (Mark Wynter) and Peter (Richard O'Sullivan) leave a party to drive out to a deserted old mansion in the middle of nowhere. Legend has it that the house is still haunted by the killer who went mad twenty years ago and killed his family in a frenzied knife attack. After daring and taunting each other with the local legend, the teenagers' laughter and high jinx turns to fear when one of them is sliced open by an unknown killer. Rather than go to the police the teenagers decide to hide the body and try to catch the murderer themselves... Behind its Forbidden Doors an Evil Secret Hides!