Plot
In 1928 England, English professor David Ash has spent most of his life working in the field of parapsychology to disprove the existence of ghosts. David was motivated by the death of Juliet, his twin sister, when they were 11, for which he blames himself. After Juliet's death, David and his mother went to live in America.
David attends a seance, where he exposes the medium's tricks, revealing her hidden accomplices. He is then shocked to hear her call out his name in a voice that sounds like Juliet's.
As a professor at Oxford, he receives a series of urgent entreaties from a Miss Webb, who claims she is being tormented by ghosts, to come and help her. The name of the house is Edbrook.
David travels to Sussex and is picked up at the railway station by Christina Mariell. Christina reveals Miss Webb is in fact their Nanny Tess, and that she wrote to David at the urging of the Mariell siblings, Christina, Robert and Simon. The siblings are concerned for her mental health and believe her belief in ghosts is due to her senility. She drives David to the palatial Edbrook House, where Christina's two brothers and the withdrawn Nanny Tess live.
David begins to perform forensic examinations of the house, trying to detect evidence of paranormal activity. Complicating the investigation is Christina's continuous flirtation with David, and his own infatuation with her. However, older brother Robert is against their friendship, and the two have a suspiciously close relationship. David begins having paranormal experiences. Christina, who had originally told David both her parents died in India, admits that in fact her mother drowned herself in the lake and Nanny Tess was the one who discovered the body. David believes it is the trauma of this which is causing Nanny Tess to see the ghost of Mrs. Mariell.
David then decides to leave Edbrook and asks Christina to come away with him. Although she refuses, they kiss and end up in making love in her bed. In the morning, when David wakes, the wind is gusting through the house, which is now cloaked in black drapes and littered with fallen leaves. He searches for Christina but instead sees the ghost of Juliet, who leads David to a cemetery. Juliet calls his attention to a tombstone which states that Robert, Christina and Simon Mariell all died in a fire at Edbrook House in 1923.
A confused David seeks out Dr. Doyle, the family doctor, whom he had met earlier, only to be told by Juliet's ghost that Doyle also had died years ago. Despite Juliet's warning, David leaves with Christina, who has appeared in her car. On the drive home, he sees Juliet in the middle of the road and wrenches the wheel to avoid her. The car crashes into a tree and explodes, killing Christina. David escapes, returns to the house and confronts Nanny Tess. She confirms that the Mariell siblings are dead and that their ghosts will do anything to keep her and David from leaving. The reason Mrs. Mariell drowned herself was because she discovered drunken Simon and Robert in their parent's bed having incestuous sex with Christina. The siblings appear and force Nanny Tess to confess to their murder (she had locked them in a bedroom and then set fire to the house).
With David as the new victim of their torments, the siblings no longer need Nanny Tess. They kill her, and Christina asks David to die for them. He tries to escape but is blocked by the three siblings and Dr. Doyle. They set the mansion ablaze, but he escapes to the upstairs bedroom. While Robert, Simon and Christina cackle within the flames at his imminent death, Juliet appears and walks through the flames, takes David by the hand and rescues him. As they walk away from the mansion's ruins, Juliet absolves him of his guilt over her death and departs to the afterlife.
David then returns home and is greeted by his assistant, Kate, as he steps off the train. Behind the unsuspecting couple, Christina moves out of the shadows and follows them through the fog as they leave the platform.
