Hampstead Heath, in the north of London, claims as two of its more distinguished residents the best-selling author of mystery novels, Charles Condomine, and his second wife, Ruth. They are preparing to entertain at dinner, and Madame Arcati is expected later to conduct one of her famous séances. After dinner Madame Arcati breezes in on her bicycle, explains the details of the forthcoming séance, and begins the session to communicate with a spirit in the unknown. The spirit is Charles’ late wife, Elvira, whose voice is audible only to Charles. Unexpectedly, Elvira, clad in a greenish cloud-like garment, flies across the room, unseen by the guests. Charles sees Elvira and has a lengthy conversation with her. He even tries to introduce her to Ruth, who is upset, thinking her husband has gone slightly daffy. Ruth storms out of the room, leaving Charles with Elvira.
The next morning at breakfast, Ruth feels that Charles’ unusual behavior was due to the effects of alcohol, but when Elvira shoves a bowl of flowers in her face, Ruth believes. Ruth goes to Madame Arcati’s coffee shop, where she is surrounded by her student spiritualists, to plead with her to get rid of Elvira. Madame Arcati has bungled the job; she doesn’t know how to do it. While Ruth and Madame Arcati are having their difficulties, Charles and Elvira reminisce about their marriage. Charles agrees to take Elvira to the Penthouse Club for old times’ sake. She tries to convince Charles to forget everything and follow her, as she describes her astral activities. Excited about the wonderful things that Elvira describes, and encouraged by her, he mounts the parapet, extends his arms in an attempt to fly, and plunges out of sight.
Ruth points out to Charles, who as a result of his plunge has a bandaged head, that Elvira is attempting to kill him off. Elvira tampers with Charles’ car, hoping to kill him when he drives it. Instead Ruth drives it first and is killed. Elvira declares her spiritual return a flop because she hasn’t been successful in bringing Charles to her world. She confesses homesickness and sings about the extraordinary environment of her "Home Sweet Heaven." Charles and Elvira arrive at Madame Arcati’s coffee shop to try to send Elvira back home. To Madame Arcati’s delight, Charles’ consternation and Elvira’s disgust, Ruth suddenly appears, fully materialized. Ruth bemoans the fact that she will have to spend eternity alone with Elvira. By mystical machinations, Elvira places an "extremely long distance call" to Merlin the Magician, somewhere in the great beyond. Merlin immediately dispenses a deadly poison, "instant" hemlock, which is poured into the brandy decanter. Charles and his two ectoplasmic wives try to make the best of an impossible situation. Madame Arcati attempts to untangle the mess. She discovers that Edith, the maid, unknown even to herself, is a natural medium. She dematerializes the two ghostly wives. As the dematerialized spirits romp around the house, playing havoc with the furnishings, Charles and Madame Arcati drink a toast to their success. The poisoned brandy acts quickly with Charles and Madame Arcati joining Elvira and Ruth in the celestial world of the unknown, where they will all fly faster than sound forever.