A young woman is laid out naked on an altar surrounded by figures in monk's garb. A man wearing robes and a goat mask leads the ceremony, invoking someone or something to enter the woman's body.

A young man, Stephen, entertains an American woman in his isolated country home. They go up to a bedroom and begin to make love, but when he becomes violent and rips off her clothes, she runs away. As she tries to leave, he crushes her head in the door, then stabs her. Another woman arrives as he is disposing of the body.

A block of high rise flats, early morning; a young couple are in bed. The man, John, presents his girlfriend, Catherine, with an early birthday gift: a bracelet which belonged to his mother. Catherine goes to her parents' house; from there they begin their journey out to the country to visit her father's brother, Alexander, who her father hasn't seen since childhood. Her father, driving, suddenly clutches his head in pain and crashes into a tree. Catherine gets out of the car, which blows up and bursts into flames. Her uncle, Alexander, and his secretary, Frances, take her into the house. Alexander's son, Stephen, announces that her parents are dead.

Frances tries to seduce Stephen, but he pulls away and storms off. The next day, on a walk round the grounds, Stephen tells Catherine that his mother died at the age of 29. Catherine has a vision of a naked woman tied to a tree being branded with a cross and whipped. Finding herself alone, she runs back to the house. Her parents' funeral is that afternoon, in a private burial ground; afterwards, she finds a grave in the woods marked 'Camilla Yorke. Died aged 20.'

Stephen and Catherine become close, making Frances jealous. That night, someone steals the bracelet given to Catherine by John. Frances and Stephen argue; she can't accept that their relationship is over.

At his flat, John cuts his hand on a broken glass. A hand places Catherine's bracelet in front of a photo of John on an altar. John gets into a lift, but a noise deafens him and the lift goes up to the top floor. John gets out, as if in a trance, and throws himself off the roof. That night, Catherine dreams about a woman being sacrificed, then sees herself on an altar covered in snakes. She wakes up and Stephen comes in; he kisses her and they make love.

The next day, Catherine tells Stephen she is in love with him and wants them to go away together, but he is reluctant to leave. Frances betrays Alexander, revealing to Catherine that he is going to try and raise Camilla Yorke from the dead as she had incredible powers and he wants her to be high priestess of his coven. His previous attempt resulted in the death of his wife, witnessed by Stephen; Alexander then realised that they needed a direct descendent, Catherine, for the ritual to work. Frances and Catherine plan to run away that night but Stephen finds out. When Catherine goes to Frances' room, she finds her dead.

Later that night, Alexander and Stephen fetch Camilla's coffin. When Catherine wakes up she finds her door locked. She tries to open it with a nail file, but Alexander and Stephen arrive, Alexander dressed in red and black robes. She is dragged out to the woods, where a group of cowled figures with torches are lighting a pyre. Catherine stabs Stephen in the eye with the nail file and runs away, chased by the hooded figures.

At the house, she bumps into her father, who tells her that she was injured in the car accident and has been asleep since it happened. Inside they find Alexander sitting by the fire. He tells her to ring her boyfriend, pointing to a curtain behind which is a telephone. When she pulls back the curtain, she sees the body of Stephen, still with the file in his eye. She tries to escape but she is trapped. Her father enters wearing robes. She screams and the ceremony begins.