When her husband disappears, Carly Hardwicke (Kim Novak) finds it impossible to rent a room in her London apartment, since everyone assumes she's a murderer. Recently arrived American diplomat William Gridley (Jack Lemmon), however, has no idea about her reputation. Sparks fly between the pair, and Gridley rents the room. When his boss, Franklyn Ambruster (Fred Astaire), learns what Gridley has blundered into, he reproves him until he meets the lovely Carly. The two men try to clear her name.