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 so...