Architect Walter Craig is invited to spend the weekend at a country house. As he meets the host, Elliott Foley, and his five other guests, he becomes increasingly unnerved. He explains that each of them, and everything he sees, is part of a dream - a nightmare - he has been having. When Craig predicts they will be joined by a brunette woman asking for money, the others are intrigued, except psychiatrist Dr Van Straaten, who insists on a rational explanation. They begin to discuss the supernatural and Granger recounts his own experience:
A racing driver, Granger suffers a serious accident. Drawing the curtains of his hospital room, he is surprised to see daylight and, in the street below, a hearse. The driver looks up at him and smiles, saying "room for one more inside." Granger's doctor reassures him that it was a delusion brought on by the accident, and he recovers well. Leaving the hospital, however, he is about to board a bus when the conductor turns to him, saying "room for one more inside." He has the face of the hearse driver. Unnerved, Granger lets the bus go. Further down the road, the bus crashes, killing all the passengers.
Van Straaten remains cynical. Soon however, they are unexpectedly interrupted by Mrs Granger, complaining she has no money to pay the taxi. Craig begins to remember his dream more fully. He predicts that later he will be driven to some unspeakable evil. Elliott's mother suggests that young Sally should go home, but relents when Sally says she has her own story to tell:
At a friend's Christmas party, Sally plays 'sardines' - a version of hide and seek. She is soon found by one boy. While the two look for a better hiding place, he tells her the house is haunted; in 1860, a young girl murdered her half-brother. When the boy tries to kiss her, Sally runs into a side room. She comes upon a small boy, Francis, sobbing. He tells her his half-sister wants to kill him. She comforts him, singing him to sleep. Rejoining the others, she discovers that Francis was the ghost of the murdered boy.
Asked to relate more of his dream, Craig remembers striking Sally violently, after Van Straaten breaks his glasses. But at that moment, Sally's mother arrives and insists she leaves. Meanwhile Joan tells her own story:
For his birthday, Joan buys her fiancé, Peter, an antique mirror. But one evening Peter sees another room reflected in the mirror. The visions continue and he fears he is going mad. Joan forces Peter to confront the mirror with her, but this time it is even worse: Peter sees only the other room, an ornate bedroom with a log fire and four-poster bed - but no Joan. With Joan's help, Peter regains control and sees the room as normal. The wedding goes ahead and Peter loses his fear of the mirror. Visiting her mother in Chichester, Joan visits the antique shop where she bought the mirror, and learns its history. It belonged to a wealthy man, crippled in a riding accident, who became insanely jealous of his wife and finally strangled her, before slitting his throat in front of the mirror. Joan returns home to find Peter angry; he accuses her of having an affair. He tries to strangle her. In desperation, Joan smashes the mirror, breaking the spell.
The other guests challenge Van Straaten to explain Joan's story. But as he begins, Craig announces he is leaving, to prevent his dream coming true. Van Straaten begs him to stay to confront his fears. Finally, Foley tempts him with a drink and a story of his own:
Golf-obsessed George and Larry are deadly rivals on the green, best friends off it, until Mary comes between them. Her inability to choose makes them miserable and puts them off their game. Finally, they decide to play a round - the loser to disappear for good. At the final hole, Barrett wins - but only by cheating. Larry accepts defeat and, to George's amazement, walks calmly into the lake to his death. But later Larry returns, as a ghost, threatening to haunt George forever, unless he gives up Mary. George reluctantly agrees but Larry has forgotten the code to return to Heaven. He is still trying to remember it on George's wedding night, as Mary waits upstairs. Desperate, George tries to help find the code but ends up disappearing himself. Larry gratefully takes his place.
The guests laugh. Challenged by the others, Van Straaten remembers an unusual case:
Noted ventriloquist Maxwell Frere entertains audiences with his cheeky dummy, Hugo Fitch. One night an American ventriloquist, Sylvester Kee, observes the act. After the show, Sylvester, invited by Hugo, goes backstage. In Maxwell's absence, Hugo suggests he and Sylvester team up. Sylvester, impressed, assumes this is part of Maxwell's act. But Maxwell appears worried that Sylvester might take up Hugo's offer. Sylvester leaves, convinced Maxwell is mad. Some time later, Sylvester witnesses a drunken Maxwell become involved in a brawl in a hotel bar. Sylvester helps him to his room, leaving Hugo propped up on the bed. Later, Maxwell bursts into Sylvester's room, demanding to know where he has hidden Hugo. Sylvester protests his innocence, but is astonished when Hugo is found. Maxwell pulls a gun, shooting Sylvester twice. In Maxwell's prison cell, Van Straaten arranges to reunite him with Hugo. Hugo apparently taunts Maxwell about his fate; Maxwell responds by smothering the dummy and stamping it to pieces. Maxwell is sent to an asylum, where the recovered Sylvester visits him. But the voice which greets him is not Maxwell's, but Hugo's.
As Van Straaten finishes his story, he breaks his glasses, confirming Craig's prophecy. Left alone with the psychiatrist, Craig is compelled to strangle him, then falls into a delirium, incorporating elements of each of the stories: in a game of 'sardines', he strikes Sally, tries to hide in the room in Peter's mirror and runs into Sylvester and the mocking Hugo. Finally, he is in a prison cell with Hugo, who advances menacingly and strangles him.
Craig wakes, shaken, in his bed. The telephone rings: it is Elliot Foley, inviting him to stay with him in the country. Approaching the house, Craig has a strange feeling that it is familiar.