In the bustling London of the 1960s, a young American, Bill (Jack Lemmon), arrives in the city seeking a fresh start and finds himself at a charming boarding house run by a mysterious owner, an alluring woman named Liz (Kim Novak). What begins as an ordinary stay quickly turns into a tangled web of intrigue when Bill discovers that Liz is at the center of a dark mystery related to her husband's disappearance.
As Bill tries to acclimatize to his new life in the city, he finds himself increasingly drawn to the enigmatic Liz, who appears to be both sweet and dangerous. But his curiosity leads him to investigate the dark history behind the boarding house, and to his surprise, he finds himself in the midst of a plot filled with deception, suspicion, and a possible murder. With the help of a British detective, Bill immerses himself in a world of secrets where all the tenants seem to have something to hide.
Blending comedy and suspense, Bill grapples with the growing reality that the woman who has stolen his heart may be involved in something far more sinister than he imagined. In a cat-and-mouse game filled with humor and unexpected twists, the film explores the thin line between love and betrayal, leaving the audience to wonder: can one truly trust appearances?