The film opens with narration over a silhouette of Hill House at night. The narrator, Dr. John Markway (Richard Johnson) tells us, "An evil old house, the kind some people call haunted is like an undiscovered country waiting to be explored. Hill House had stood for 90 years and might stand for 90 more. Silence lay steadily against the wood and stone of Hill House. Whatever walked there walked alone." Title and credits follow, then narration continues, "Scandal, murder, insanity, suicide: The history of Hill House was ideal. It had everything I wanted..." The house was built in New England by a man named Hugh Crain for his wife and young daughter. A horse and carriage accident took the life of the first Mrs. Crain (an uncredited Pamela Buckley) before she even saw the house. Hugh Crain (an uncredited Howard Lang) and young daughter, Abigail (an uncredited Janet Mansell) said a few words over the body, but Hugh was left an embittered man. Crain married again, and the second Mrs. Crain (an uncredited Freda Knorr) also died, falling down the main staircase. Hugh Crain left Abigail with a nurse (an uncredited Susan Richards) and went to England where he died in a drowning accident. Abigail kept the same nursery room her entire life. By the time she was eighty (an uncredited Amy Dalby) she was a bedridden invalid. Her nurse-companion (an uncredited Rosemary Dorken) was a local girl and, it is with this young companion the evil reputation of Hill House really begins. The old lady died while calling for help. The companion was trysting on the verandah with a farm hand. The companion inherited Hill House and occupied it for many years, but eventually hanged herself. The house then passed to a distant relative, named Mrs. Sanderson (Fay Compton).
Markway visits Mrs. Sanderson where he convinces her to let him use the house for psychic research. He explains, "I shall occupy the house with a group of carefully selected assistants...I must have specially qualified help to take notes and document any evidence of the supernatural I may find." Eldridge Harper (Ronald Adam), Mrs. Sanderson's lawyer, voices his concern about publicity seekers and the propriety of having women in the house. Harper suggests to Mrs. Sanderson that her nephew, Luke, joins the doctor at Hill House, as he expects to inherit the property. Mrs. Sanderson asks point blank, "Exactly what do you and your assistants expect to find at Hill House?" Markway replies, "Maybe only a few loose floorboards, and maybe, I only say maybe, the key to another world."
Dr. Markway, taking a leave of absence from his university professorship, finalizes his list of assistants. Only two end up accepting, Eleanor Lance and Theodora (no last name).
Eleanor Lance (Julie Harris) is living with her sister. She is nearly broke and weary after looking after her invalid mother non-stop for eleven years. Mother is now dead, and she fights with her sister over just about everything. She begs to use the car, which is after all, half hers. Her brother-in-law, Bud Fredericks (an uncredited Paul Maxwell) tries to act as mediator between Eleanor and his wife, Carrie (Diane Clare). He is sympathetic to Eleanor's plight, but their daughter, Dora (an uncredited Verina Greenlaw) takes her cues from her mother, and taunts her Aunt Eleanor. On the vacation plan, Bud sides with Eleanor, "I think you should have a vacation, Nell." Carrie objects, but Eleanor is not to be deterred and she shows her family how she reacts when pushed to her breaking point. She is normally quiet and meek, but when pushed is loud and assertive.
Nell decides to take the car and confronts the garage attendant (an uncredited Claude Jones) for the keys. She departs Boston along U.S. 50 and Route 238 to Hill House. We hear Nell thinking and she reveals she will never return to live with her sister. In fact, most of what we learn of Eleanor is hearing her thoughts.
Eleanor arrives at Hill House. The property is surrounded by a stone wall and the entrance by a tall, iron spiked, gate. She honks the car horn, and Mr. Dudley (Valentine Dyall), the cranky caretaker, finally deigns to respond. "What do you want?" he asks. Eleanor explains that she is expected. After an impertinent exchange with Eleanor, Dudley finally opens the gate and allows her to enter the property. Eleanor is the first to arrive and drives up to the house. Along the way she stops to look at it. It is a huge, stone mansion with lots of detail on the façade and steep, pitched roofs. Her first reaction is that the house is vile and it is staring at her. She carries her suitcase to the front door and is greeted by Mrs. Dudley (Rosalie Crutchley). Mrs. Dudley reluctantly allows Eleanor to come inside, but does not utter a word to her.
The inside of the house is dark and over-decorated, and Eleanor is escorted to her room. Mrs. Dudley explains the house rules about meals, and that she won't stay in the house after dark. Eleanor checks out the bathroom and hears the next guest arrive. Theodora (Claire Bloom) introduces herself. Eleanor explains they share a bathroom. Mrs. Dudley repeats her meal and departure rules by rote, but Theo and Nell ignore her. Theodora is a bit strange to Eleanor (Theo clearly flirts with Eleanor throughout the film) Theodora's sexual orientation is only hinted at, and we later learn she has the gift of ESP. Theo and Nell explore the house, but they get lost. Both women feel a chill, and Nell observes, "The house, it's alive." Theo seems to feel that the house wants Nell.
Dr. Markway appears and explains he left the door opened, but it closed itself. Markway gives the women a tour of part of the house, starting with the main purple parlor, which they will use as an operations center. He explains that all the doors were set slightly off-center, so they close themselves. Despite studying plans to the house, even Markway gets lost on his way to the dining room. They hear a noise, but it turns out to be Luke Sanderson (Russ Tamblyn) mixing a pitcher of martinis as he enters the dining room. Luke serves each person a martini. They sit down for dinner and discuss their duties and responsibilities. Markway explains that Theo was accepted because of her remarkable power of ESP and Eleanor had a poltergeist experience as a child, "showers of stone fell on your house for three days when you were 10 years old." Luke is a non-believer. His interest is to financially exploit Hill House, after he inherits it, of course.
That evening, in the parlor, Markway works on his notes while Eleanor sits quietly on the couch. Theo and Luke play gin rummy at the game table. Theo's ability to see cards allows her to win five games in a row, much to Luke annoyance. She demands he pay her the $12 he owes, but he refuses because she cheated. The four decide to turn in for the night and continue the tour the next morning. Markway gives them papers and asks that they complete them with their observations each night.
Sometime during the night, Eleanor wakes, and still in a near dream state, thinks she hears her mother knocking on the wall. Theo hears it from the next room also and calls to Nell. The two women are frightened and both hear the pounding noise. It comes and goes, but louder each time. They finally hear a woman shrieking and laughing that fades away. When Nell opens the door she sees Luke and Markway in the hall outside. The men explain they were chasing a dog and followed it outside, but they did not hear the loud noises the women heard. Markway concludes that something is trying to separate the men and women.
The next morning, Markway and Nell join for breakfast. Nell is starting to develop romantic feelings for John Markway, unaware that he is married. She tells him that she spent eleven years taking care of her invalid mother. Nell also voices her fear that she will be turned out of Hill House with no where to go. Markway tells Nell how he came to do psychic research, and that his family disapproves. Theo joins the pair and warns the doctor, "If anyone gets hurt, it's going to be your fault, Markway." Markway explains that no one has ever been physically hurt by a ghost. Luke enters and directs his companions to something he saw in the hall. Someone or something has handwritten a message in chalk on the wall. It says, "Help Eleanor Come Home." Eleanor reacts strongly. She first accuses Theo of playing a cruel joke. The two women bicker and Markway postpones the tour and tells Theo to take Eleanor to her room.
The tour starts with the greenhouse. A large stone sculpture sits in the center of the room. It is supposed to be St. Francis curing the lepers, but Luke thinks its a family portrait of Hugh Crain and his wives and daughter. Suddenly, the door slams open and a gust of wind moves the plants. They approach the library, but Nell refuses to enter. The smell reminds her of her mother's sick room. Prominent in the room is a very tall, wrought iron, spiral staircase. Markway points out that the balcony high above is where the companion to Abigail Crain hanged herself. Luke climbs up a few feet on the staircase, but jumps back to the ground when it starts to sway and shake.
Eleanor ventures out to the verandah and nearly falls over the balcony as she looks up to the tower above the library. Markway threatens to send her home, but Nell begs to stay. Markway suggests Theo and Nell share a bedroom... "like sisters". That evening, the two women discuss their lives and plans for the future. Nell makes up a story about having an apartment of her own. Just when Theo is about to make a move onto Nell, Markway calls them and Luke into the hallway outside the Nursery. He has discovered a cold spot. He invites all to experience the phenomenon. He gleefully explains, "A cold spot, a genuine cold spot. I guarantee it won't register on any thermometer." Luke dismisses it as just a draft, but Markway says it is the heart of Hill House: The Nursery.
In the middle of the night, Nell awakens. She hears a little girl laughing. She asks Theo to hold her hand, as their two beds are almost touching. The laughter continues and Nell complains, "Theo, you're breaking my hand." The laughs turn to wimpering and Nell complains that something is hurting a child and she won't allow that to happen. She yells, "Stop It!" Theo turns on the light and we see Nell is on a day bed about twenty feet from the bed Theo occupies. Nell stares at her hand and asks, "Whose hand was I holding?"
The next morning, Markway is in the music room and checks his watch and makes a note about the harp playing itself. Nell enters the room and asks about how it could play itself. Markway explains that it may be preternatural: Something we don't have any natural explanation for right now, but probably will have some day. Nell voices her fear that it is all in her imagination and concludes she may be going insane. She is haunted by the circumstances of her mother's death and that she may somehow be responsible. They both hear the harp play a note and Markway again checks his watch and makes a note in his paperwork.
That evening, Luke finds a disturbing book that Hugh Crain made for his daughter, Abigail. Nell and Theo bicker and Markway notes that everyone's nerves are on edge. Theo continues to flirt as well as needle Nell, this time about a budding romance she fantasizes about with John Markway. Nell runs away and Theo catches up to her, and tells Nell that is he is making a fool of herself in thinking that Dr. Markway will ever get involved with her. Nell accuses Theo of being an "unnatural thing" as well as a "nature's mistake."
At that moment, a car horn honks and a taxi pulls up in front of the house. Grace Markway (Lois Maxwell), John's wife, arrives. She informs her husband, "A reporter's been telephoning all day. He's on your track. He's heard about you renting this place." Grace begs her husband to abandon the house and his research. When John refuses, Grace pays the driver, grabs her suitcase and announces she is staying at Hill House, "to join the ghost hunt." When Eleanor casually mentions the nursery as a place to stay, Grace quickly accepts the challenge, "Thank you, my dear. The nursery it is." Markway and Nell try to dissuade her, but Grace responds, "You insult my intelligence. You don't think I'd believe anything you ghost hunters might tell me." Luke notices the door to the nursery is open for the first time. Grace decides to spend the night in the room, despite everyone's warning not to. Markway insists he and the three researchers spend the night downstairs in the parlor.
Later that night, Nell and Theo sleep together on the sofa by the fireplace as Markway sleeps in a chair. Luke finishes his tour upstairs and enters the parlor. He heads for a bottle on the mantle. Suddenly, the parlor door slams shut by itself and the others wake with a start. They hear a deep rhythmic banging outside the door. Markway is concerned about his wife upstairs. Next a very loud banging comes from just outside the door. The unseen phantom presses against the parlor door as it bows inward and out like breathing, creaking and crunching against the hinges. The sound moves to overhead towards the nursery. Markway is desperate to check on his wife.
Unseen, Nell runs from the parlor, through the music room, and upstairs directly to the nursery room. The doors are open, but Grace Markway is nowhere to be seen. Her bed shows signs of being used. Markway and the others arrive and start the search. Nell wanders away. She finds herself in the greenhouse. Descending into her own little world, Nell dances out onto the verandah. When she hears the others calling to her, Nell runs into the Library. She is drawn to the spiral staircase and the balcony at the top. Before she reaches the top, the rickety staircase begins its swaying, the lateral support bolts pulling away from the wall. Markway calls to her, begging her to carefully walk back down. She ignores him and stands on the balcony. Markway carefully climbs the stairs and joins Nell on the iron balcony platform. Before they walk back down, Nell sees Grace Markway peer at her through a trap door in the ceiling.
A little later, Markway is furious and now insists Eleanor leave the house for her own safety. Luke brings her car around and Theo packs her bag. Nell tries to talk them out of her dismissal, but the three insist she leave. They escort Eleanor out to her car. Luke gets back out of Nell's car to retrieve the gate key from Markway. She drives off without Luke. Before she reaches the gate she is distracted by the white-robed figure of Grace Markway and crashes into a tree.
The three find Eleanor dead in the half overturned car. She crashed into the same tree that killed the first Mrs. Crain. Grace wanders over to the accident scene. She explains to her husband, "I didn't want any of this to happen. You must believe me, John." She explains that she woke and was frightened. She got lost looking for her husband and ended up in the attic. While Theo blames Grace for Eleanor's accident, Luke takes a different view. "Eleanor did it to herself. It looked to me, anyway, like she deliberately aimed the car at this tree." Markway blames the house. Luke stares at the house and remarks, "It ought to be burned down and the ground sowed with salt."
We close with an evening shot of Hill House with Eleanor, now a ghost, narrating from beyond the grave about Hill House and that "we who walk here... walk alone." The end title comes up as well as the final title card 'The Haunting' followed by eerie piano music.