Kit (Day), an American married to wealthy London businessman Tony Preston (Harrison), is terrorized by a mysterious voice. She first hears the voice as she walks in the thick London fog. Then she hears the voice over the telephone, threatening to murder her. While on a shopping spree, Kit is nearly killed when someone pushes her in front of a bus. Nevertheless, Tony, Kit's visiting aunt Bea (Loy), and even Scotland Yard refuse to take any of these incidents seriously. Kit gets sympathy from Brian Younger (Gavin), a construction foreman, but his occasional strange behavior suggests that he may be the secret tormentor. Also suspect is Malcolm (McDowall), the pesty son of Kit's servant, who worships his father's employer. The tension builds until the climax which takes place atop a towering scaffolding. The film's ad campaign warned audiences not to reveal the "unique plot developments." While nothing to rival Hitchcock, the film's look and direction make it a worthwhile effort. Doris Day makes the switch from light comedy to suspense fairly well, creating a believable victim, while Harrison, his usual debonair self, adopts a sinister air. Day undergoes no fewer than 17 costume changes, for which designer Irene received a well-earned Oscar nomination.