No sooner does American Kit Preston (Doris Day) travel to foggy London with her new husband, the oily Anthony Preston (Rex Harrison) than she starts to receive threatening calls from a nasty-whispering man who promises to kill her. Of course, she is unnerved by the calls, but there is reason to believe they are really happening, though everyone thinks she is losing her mind. Fortunately, Kit has her trusty Aunt Beatrice Corman (Myrna Loy) on hand for support. On the downside, Inspector Byrnes (John Williams) is a bit cynical on the surface about the threats. Husband Tony remains stalwart, even when Kit seems to find herself surrounded by dubious people like Malcolm (Roddy McDowall) and Charles Manning (Herbert Marshall).