Dr John Markway narrates the history of the 90-year-old Hill House, which was constructed in Massachusetts, United States, by Hugh Crain for his wife. She died when her carriage crashed against a tree as she approached the house for the first time. Crain remarried, but his second wife died in the house from a fall down the stairs. Crain's daughter Abigail lived in the house for the rest of her life, never moving out of the nursery room. She died calling for her nurse-companion. The companion inherited the house, but hanged herself from a spiral staircase in the library. Hill House was inherited by Mrs Sannerson, a distant relative of the companion, although the house has stood empty for some time.
Markway wishes to study the reported paranormal activity at Hill House and sends invitations for people to join his investigation; Mrs Sannerson demands that Markway allow her heir Luke Sannerson to join. Only two other individuals accept—Theodora, a psychic, and Eleanor Lance, who experienced poltergeist activity as a child. Eleanor has spent her adult life caring for her invalid mother, whose recent death has left Eleanor with severe guilt.
The group find the mansion's walls were constructed with angles askew, resulting in off-centre perspectives and doors that open and close by themselves. During their first night in the house, Eleanor and Theo are terrified by banging sounds made against the door, and hear menacing laughter. Luke and the doctor, however, report the house had been silent for them. In the morning, the words "Help Eleanor come home" are found scrawled on a wall, distressing Eleanor. The group explores the house, discovering a huge marble composite statue, supposedly of St Francis curing lepers, which seems to echo the string of characters who have lived in the house (Hugh Crain, Abigail and the companion), but also resemble Dr Markway, Luke, Theo and Eleanor.
The doctor, Luke and Theodora explore the library with the treacherous spiral staircase, but Eleanor has a severe reaction that prevents her from entering. Leaning over the veranda to look at the library's tower, she becomes dizzy and is caught by Markway, who speculates that he should send her home, but Eleanor protests. Dr Markway discovers a cold spot outside the nursery room. Despite these occurrences, Eleanor feels an affinity to Hill House.
That night, on Markway's insistence, Theo moves into Eleanor's room, and they fall asleep in the twin beds pushed together. Eleanor is awakened by the voice of a man speaking and a woman laughing. Fearful, she asks Theo to hold her hand. As she hears the sound of a girl crying, she shouts. Theo awakens to find that Eleanor has moved from the bed to the couch, and Eleanor realises it was not Theo's hand she held.
The following day Theo confronts Eleanor about her feelings for Dr Markway, and Eleanor lashes back at Theo for being "unnatural," implying either Theo's psychic ability to know what Eleanor is thinking or her attraction to Eleanor. Dr Markway's sceptical wife Grace arrives with plans to join the group for the duration of the investigation, to the consternation of Eleanor, who had begun developing feelings for Markway while unaware that he was married. Grace demands a room in the nursery despite her husband's warning that it is likely the centre of the disturbances. That night in the living room, the group experiences loud banging and an unseen intruder attempting to force its way into the room, causing the door to bulge inward. The banging moves toward the nursery, and Dr Markway pursues it as does Eleanor by using a different exit from the living room. Mrs Markway has disappeared and then Eleanor splits off from the group. Her instability worsens as she enters the library and climbs the spiral staircase, followed by Markway, who tries to coax her down despite the stairwell coming loose from the wall. At the top, Eleanor nearly falls to her death whilst glimpsing Grace above her. Markway grabs her and saves her. No-one believes she saw Grace.
Markway insists Eleanor leave but she pleads to stay, convinced the house wants her. If she leaves she thinks Grace will take her place. Eleanor drives off toward the front gates. The steering wheel begins to turn by itself, and she surrenders to the unseen force. A female figure suddenly appears in front of the car, causing Eleanor to crash into a tree and die. Markway and the others arrive to find that the figure is Grace, who says she woke in fear and tried to find her husband but the house kept her lost. She ended up in the attic when she was trying to find a way back, and Eleanor saw her through a trapdoor hatch. She is unsure of how she found her way outside. Luke observes that Eleanor deliberately aimed the car at the tree, but Markway asserts that something was in the car with her. He notes that the tree was the same one where Mrs Crain died. Theo remarks that Eleanor got what she wanted—to remain with the house. Convinced of the supernatural forces he once scoffed at, Luke says about the house, "It ought to be burned down and the ground sowed with salt."