Eccentric millionaire Frederick Loren (Vincent Price) invites five people to a party he is throwing for his fourth wife Annabelle (Carol Ohmart) in an allegedly haunted house he has rented, promising to give each $10,000 with the stipulation that they stay the entire night in the house after the doors are locked at midnight.
The guests are test pilot Lance Schroeder (Richard Long), newspaper columnist Ruth Bridges (Julie Mitchum), psychiatrist Dr. David Trent (Alan Marshal) who specializes in hysteria, Nora Manning (Carolyn Craig) who works for one of Loren’s companies, and the house’s owner Watson Pritchard (Elisha Cook). All are strangers to both the Lorens and each other, with their only commonality a desperate need for money.
The Lorens have a tense relationship; Frederick is convinced Annabelle tried to poison him in order to acquire his wealth, which Annabelle firmly denies, attributing his suspicions to paranoia and jealousy. Pritchard believes that the house is genuinely haunted by the ghosts of those murdered there, including his own brother. He gives a tour of the house, including a vat of acid in the basement which was used by a previous resident to kill his wife.
When Lance and Nora remain behind to further explore the basement, Lance is locked in an empty room and struck on the head, while Nora is confronted by a menacing figure she takes for a ghost.
Annabelle privately warns Lance that her husband is scheming something, and that she suspects him of murdering his second and third wives. Gathering downstairs, the guests are told the rules of the party, and each is given a .45 ACP caliber pistol for protection. Having encountered further apparitions, Nora decides against staying the night, but the caretakers lock the doors five minutes early, taking that option out of the guests’ hands.
Lance is confronted by Nora, who tells him an unseen assailant strangled her and left her for dead. In light of Annabelle’s warnings, they both suspect Loren. He tells her to remain out of sight so that her attacker will still think her dead. Hearing a scream, Lance and Dr. Trent find Annabelle’s corpse, suspended to suggest she hanged herself, but the absence of a perch immediately arouses suspicions of murder. To survive the night, Lance and Dr, Trent propose that everyone stay in their rooms and shoot anyone who enters; thus the innocents will have no reason to leave their rooms, and the killer must stay put or admit his guilt.
Nora is chased from her room into the basement by Annabelle’s ghost. Aroused by the ghostly sounds, Trent concludes that the killer is about and proposes he and Loren split up to search the house. Lance uncovers a secret room at the end of the second-floor hall, but once he enters the door shuts behind him, trapping him. Trent instead meets with Annabelle, who had faked her death using a hanging harness and sedatives.
Secretly lovers, the two of them have orchestrated the various mishaps in order to manipulate Nora into killing Loren. Nora, seeing Loren enter the basement with a gun in his hand, does indeed shoot him. After she flees, Trent slips in to dispose of Loren’s body in the vat of acid. The cellar (or possibly the film itself deliberately) goes dark, there is a choking sound, a splash and the sound of dissolving in the acid.
Annabelle walks to the now dimly-lit basement to confirm her husband is dead. All the doors mysterious swing shut and a skeleton rises from the acid, accuses her in Loren’s voice, and pursues her. As she backs away from it to the edge of the acid vat, it reaches out a hand and pushes her; off-balance, she falls into the vat. Loren emerges from the shadows, holding the puppeteer control unit that he used to manipulate the skeleton (the dim light concealed the wires) and revealing that he had known their plot all along.
After Nora, Pritchard and Ms. Bridges release Lance from the secret room, Nora tells them that she shot Loren. When they arrive in the cellar, Loren explains that he had loaded her gun with blanks, that Trent and his wife plotted to kill him, and that they both met their end in the vat of acid. He also implies that he will claim self-defense and, although responsible for their deaths, will not be convicted. Pritchard remains convinced the house is haunted, with Trent and Annabelle now added to its ranks of ghosts, and that he will be the next victim.
“House on Haunted Hill”