In 1920s England, a group of upper-class people take part in an automobile race to Land's End. One couple, Billy and Daphne, get lost in heavy fog and run out of petrol. Billy goes to look for fuel, but takes so long that Daphne strikes out on her own. She eventually locates a rural estate owned by Dr. Lawrence, a former priest. He receives her kindly and sends his disturbed gardener, Tom, to find Billy. Tom finds and murders Billy, and pushes the car into a ravine; it is implied that he acted on his employer's orders.
Meanwhile, Dr. Lawrence tells Daphne about a trip his family took to India; his experiences with certain cults there so horrified him that he renounced religion in general. This decision was heavily influenced by the fate of his wife and son, who were converted to a new faith by a local nobleman. The former was afterwards so horrified by the things she had done that she committed suicide. Still waiting for Billy, Daphne falls asleep in a guest room. Seeing this, the doctor's Indian housekeeper, Ayah, goes to the house's attic and lets out a bloated, bloodstained man in a priest's mantle. He kills Daphne with a sacrificial knife, and Ayah ritually cooks the girl's flesh for him to eat and burns the girl's clothes.
The first couple's friends, Geoffrey and Angela, learn of Billy's death from the police and set out on a private mission to find Daphne. They too wreck their car in the fog and are separated in the search for help. The local police refuse to search the marshland as it is too dangerous. Angela locates the Lawrence estate first, and is abducted by Tom, who obviously hopes to rape her. When Dr. Lawrence discovers her presence, he reluctantly decides to offer her as another sacrifice to the ghoul in his attic. She is saved from molestation when Tom is sent out to get rid of Geoffrey, who also found the house and was convinced by Dr. Lawrence that Angela and Daphne were both conveyed safely back to town.
Tom botches the attempt to kill Geoffrey, and is half sucked into a bog in his attempt to flee. Ordered to explain himself before he is rescued, he admits that Daphne was fed to something living in Lawrence's house. Geoffrey returns to the estate and confronts Lawrence, who admits that the ghoul is his own son; the man has been a cannibal ever since his conversion, and Ayah is another cult adherent who came from India to prepare his food. The agonized Lawrence has tended to and protected his son because he promised his wife he would do so.
Geoffrey barges into the attic and confronts the ghoul, who kills him. Meanwhile, Tom sneaks into the room where Angela is imprisoned and again tries to assault her. He is interrupted and killed by the ghoul, who has gotten out of control. The creature rounds on Angela, but Lawrence enters with a pistol and fatally wounds it. Angela runs screaming from the house. Dr. Lawrence, his heart broken by what has happened, goes to his study and shoots himself through the head.Peter Cushing as Doctor LawrenceJohn Hurt as Tom RawlingsAlexandra Bastedo as AngelaGwen Watford as AyahVeronica Carlson as Daphne Wells HunterDon Henderson as The GhoulIan McCulloch as GeoffreyStewart Bevan as BillyJohn D. Collins as "Young Man"Dan Meaden as The Police Sergeant
This was the second film produced by Tyburn Film Productions. It was shot on location at Pinewood Studios, Iver Heath, Buckinghamshire, England from 4 March 1974. While the film was in production, actor Peter Cushing went through emotional turmoil: before he signed on to do this film, he lost his beloved wife Helen to natural causes, leading him to wish he would die himself and soon. According to Veronica Carson, Director Freddie Francis made Cushing do multiple takes during the scene where he talks about his love for his late wife. This caused Cushing great distress and reduced the widowed actor and some of the crew to tears. Cushing played other men who lost family members in other horror films in the 1970s, including the 1972 film Asylum and the 1973 film The Creeping Flesh.