Charles, a writer, has invited a local medium, Madame Arcati, to hold a séance at his house, as research for his new book. Both Charles and his wife Ruth have been married before, but their previous partners died. Charles' first wife, Elvira, has been dead for seven years.
The local doctor and his wife are also invited to the séance, which is preceded by cocktails and dinner. Madame Arcati arrives. She is absent-minded and eccentric. She rejects the use of Rachmaninov to set the right mood and selects a recording of a popular song, 'Always', despite Charles' faint objections. Madame Arcati's 'control' is a seven-year old girl with adenoids called Daphne.
Madame Arcati goes into a trance, shrieks and then faints. A woman's voice is heard in the room - it is Elvira. Charles denies that anything happened, but when Madame Arcati recovers she is certain that she did summon a spirit. When she has left, the other guests dissolve with laughter, but Elvira materializes, unseen by anyone but Charles. Ruth thinks that Charles must have gone mad, and goes to bed in a temper, leaving him alone with Elvira.
Elvira says that Charles must have summoned her back from the dead and what does he propose to do about it? They reminisce about their volatile marriage. Although Charles cannot touch Elvira, they spend the rest of the evening together. When Ruth awakes the next morning, Charles is not in his bed, but asleep on the living room sofa. He is very cheerful at breakfast, but Ruth is cross and accuses him of having been drunk the night before. They are still quarrelling at lunchtime - and at dinnertime. After dinner, Elvira reappears. Charles tries to convince Ruth of Elvira's presence by asking her to move objects around, but Ruth sees only the moving things and flees from the room, terrified.
The next morning, Ruth goes to see Madame Arcati, to tell her what has happened and ask for her help, while Charles and Elvira go out for a drive. Madame Arcati confesses that she does not know how to get rid of Elvira, and Ruth, annoyed, offends her by explaining the reason for her invitation to the house in the first place.
Charles tries in vain to keep peace between the women in his household. Ruth returns from an outing to find her cook, one leg in bandages, leaving, and her maid Edith in bed with a bandaged head. Elvira is sitting innocently on the stairs. Ruth discovers that the gardener and Charles himself are also injured. Ruth tells Charles that she thinks Elvira is trying to kill him, so that they can be together. She drives off to see Madame Arcati again and Elvira is horrified, because she has tampered with the car. It crashes and Ruth is killed. She returns to the house as a ghost and begins tormenting Elvira.
Madame Arcati telephones Charles with good news; she thinks she has found the answer to the problem. Charles declines her help. Elvira is now thoroughly miserable and quarrels with Charles, telling him she wants to leave. Charles and Elvira go to see Madame Arcati, who tries a spell to exorcise Elvira - but Ruth appears instead. All four of them return to Charles' house and try again - several times - but without success. Madame Arcati suddenly realises that it was Edith the maid who summoned Elvira, and that she was the other psychic in the room on the night of the séance. She hypnotises Edith, who makes Elvira and Ruth disappear, but their presence still haunts the house. Madame Arcati urges Charles to go away for a while. As he drives away, the car crashes. Charles, now dead, joins Elvira and Ruth, who are waiting for him. He has become another 'blithe spirit'.
