An eccentric millionaire, Fredrick Loren, who is throwing the "party" for his fourth wife, Annabelle, invites five people to a secluded masion with the offer to spend one night in his house which is haunted, with the stipulation that the power will be out and all doors will be locked at midnight, allowing no accessible escape. Anyone who stays in the house for the entire night, given that they are still alive, will each receive $10,000.
The five guests all arrive in separate funeral cars with a hearse leading, which he explains may be empty now, but they may be in need of it later. He explains the rules of the party and gives each of the guests a .45 caliber pistol for protection. Loren's wife tries to warn the guests that her husband is psychotic, causing them to be very suspicious of him, especially Nora Manning, who becomes convinced that he's trying to kill her when she keeps seeing mysterious ghouls, including the ghost of Annabelle, who had hanged herself after being forced to attend the party.
After being driven into a fit of hysteria by the ghosts haunting her, Nora shoots Mr. Loren, assuming he is going to kill her. Dr. Trent, another guest, tries to get rid of the body by pushing it into acid, but the lights go out, and when they come back on, both of the men are gone. Annabelle emerges, having faked her death with the help of Dr. Trent, and having apparently tricked Nora into killing Loren. Suddenly, a skeleton emerges from the acid accompanied by the voice of Loren. The spectre approaches Annabelle as she recoils in terror. In this panic, the screaming Annabelle accidentally backs into the acid herself. The real Mr. Loren walks out of the shadow, holding the contraption that he was using to control the skeleton of Dr. Trent. In his triumph, he watches Annabelle disintegrate.
Nora tells the other guests that she's shot Loren in the cellar, and they all rush down there. When they arrive, they see that he's actually alive, and he explains to them that his wife and Dr. Trent were having an affair, and that the "haunting" was just a joke planned by him with the help of the caretakers. He also tells them that they'd planned to trick Nora into murdering him so that they could get away with his money. He had not loaded Nora's guns with bullets, but blanks. Just when everyone thinks the trauma is finally over, Mr. Pritchard, the house owner, looks up, a terrified expression on his face, and announces that the ghosts of the house are finally coming for them.