A young woman recovering from a nervous breakdown moves with her husband to a boys' school, and finds herself being terrorized by a mysterious one-armed man, but nobody believes her.
In London, twenty-two year-old Peggy Heller (Judy Geeson) meets and marries school teacher Robert Heller (Ralph Bates) after recovering from a nervous breakdown. Robert works in the countryside in a private school owned by headmaster Michael Carmichael (Peter Cushing), who is married to Molly Carmichael (Dame Joan Collins). On the eve of moving to the country with her husband, Peggy spends the night at the boarding house of Mrs. Beamish (Gillian Lind) and is attacked by a man with a mechanical arm in her room. Mrs. Beamish calls the doctor, but they do not believe Peggy. The next morning, she heads with Robert to the country and moves into the cottage in the school. Soon, Peggy is attacked by the same man, but Robert does not believe her. Then she meets the Headmaster and realizes that he has a mechanical arm. What will happen next?—Claudio Carvalho, Rio de Janeiro, Brazil
A young woman Peggy (Judy Geeson) packs her belongings as she tells her employer Mrs Beamish (Gillian Lind) she is resigning to get married to teacher Robert (Ralph Bates). A hand appears at one of her windows, opening it. Robert telephones her and they speak. After hanging up, Peggy goes to close the open window but a hand in a black leather glove grabs her neck and starts to strangle her. In the struggle a prosthetic arm falls to the floor and then she loses consciousness.
When she awakes Mrs Beamish and a doctor (James Cossins) are with her. They say no-one was there and don't believe her story. She's had a nervous breakdown in past.
In a flashback, Peggy talks to a doctor about her time in hospital and another patient she shared a room with who felt she was being followed.
Later Peggy meets Robert who reassures her that the man will be caught and not to worry. They chat about their future and the house in which they will live together. They proceed to Robert's new school and he shows her around the schoolhouse, a large old Tudor style building in need of some repair, in which some of the furniture is covered in dust sheets.
They go into their cottage, which is next to the schoolhouse, where Robert takes a telephone call from headmaster Michael Carmichael (Peter Cushing).
That night Robert awakes but Peggy is not in bed. She is in the living room looking out of the window. Robert says maybe she heard Michael who often walks around at night.
In the morning, Michael goes out to work. Peggy explores the big old schoolhouse, passing through the dining room, dormitories, and so on. She hears the sound of children's voices and the headmaster's coming from downstairs and goes to investigate. When she opens classroom door there is no-one there and the sound stops. The headmaster suddenly appears behind her, introduces himself and offers to show her around.
In the gym he suggests she lets her hair down. He assists her, revealing he is wearing a black leather glove and has a prosthetic arm. Peggy does not see though because he is standing behind her. Michael tells her Robert needs to be away at a conference next day.
Peggy returns to cottage thinking Robert has returned. A hand in a black leather glove with a prosthetic arm attacks her again and she passes out. She wakes up in bed with Robert beside her. She tells him what happened but he doesn't really believe her.
In another flashback, Peggy talks to the doctor again about an incident when someone put something in her drink, which she could not have imagined.
Peggy is very upset with what is happening to her but she and Robert decide not to call police.
Peggy accompanies Robert as he works outside on the school grounds. They are using Michael's Land Rover to get around which has a shotgun mounted on the back. Robert parks and goes to work while Peggy walks into woods. She sees a rabbit directly in front of her but it is suddenly shot. Molly Carmichael (Joan Collins) appears with a shotgun and tells her it is private property and she could have been shot. Robert appears and introduces Peggy to Molly, saying she is the headmaster's wife. Molly tells Robert he has to attend the conference in London alone and Peggy and Robert drive off.
Robert leaves Peggy at their cottage to go and see Michael. Molly arrives with the dead rabbit and gives it to Peggy. They chat, but Molly is quite condescending to Peggy. Robert returns and says he will be staying in London overnight.
Robert leaves for London leaving Peggy alone. She fetches the shotgun from Land Rover and brings it into cottage. She hears a noise in another room and goes to investigate carrying the shotgun. There is a curtain blowing in the breeze but no-one there. Suddenly Michael's gloved hand switches on the light and she shoots him. As she walks past he grabs her ankle but she gets away and runs to schoolhouse. There is a lot of noise of children's raised voices but no-one there. Michael is following her as she runs through the school. She locks herself in a dormitory. Michael's voice shouts for silence and all the noise stops. Michael punches a hole through the locked door, unlocks it from the inside and enters the room. She shoots at him again but he only turns his head away. When Michael looks back, the lenses in his glasses are shattered. Peggy passes out.
Robert returns home but can't find Peggy in the cottage. He searches the schoolhouse and finds Peggy in the dormitory. She acts nonchalantly and won't tell him anything that happened. Robert notices the hole smashed in door and blood on floor.
Back in the cottage, Robert notices a red stain on carpet then notices the shotgun in the house and that it has been fired twice. Peggy denies anything significant happened, says she doesn't recall what the stains are, and that she had been practicing with the gun at the boathouse.
Robert looks round schoolhouse. He sees Peggy watching him from the cottage. He notices a cupboard concealing a passageway in schoolhouse. He also goes to boathouse but finds nothing so he is unable to understand what happened with Peggy and the gun.
Robert tells Peggy that it is no longer a school. He explains there was a fire in schoolhouse in 1963. Michael was badly burned and is tormented because of the children who died. He says he met Michael in hospital and agreed to help him restore the school but there are no pupils. Michael just walks around the school playing recordings and Robert assists him. Robert wants to know the truth about what happened between Michael and Peggy but she will not say anything.
Robert goes to see Molly. It transpires Molly and Robert are in love and they were the gloved hands that attacked Peggy in a plot to get Peggy to kill Michael. If they can force Peggy to confess she killed Michael, they will inherit Michael's money. They try to force Peggy to say where Michael's body is but she won't. They forge a confession letter from Peggy but neither want to sign it. Molly says she will find Michael's body if Michael will sign. He practices Peggy's signature and then signs the confession letter as Peggy, but she still won't tell Robert anything.
A bell starts ringing so Peggy and Robert go to schoolhouse. The bell stops and the schoolhouse seems empty. Michael's voice starts talking to Robert over the loudspeaker. Michael says he knows all about Robert and Molly, the gun was loaded with blanks, and the stains were made with the dead rabbit's blood. Robert fires the shotgun at some draped furniture thinking it is where Michael is hiding. Blood appears but when he removes the cover, Robert sees it is Molly gagged under the cover that he has shot. Robert angrily knocks over pieces of furniture then grabs Peggy and runs out with her. He takes a rope tied in a noose from the gym and puts it over a tree branch. A hand in a black glove appears and grabs Robert by the throat.
Later the police arrive and ask for Mr. Carmichael. There is the sound of a piano and school children singing coming from schoolhouse. Robert is hanging from the tree.
