In the scenic French countryside, the Paris-Bordeaux express races along when, out of nowhere, a dead man, dressed only in pajamas and a bathrobe, unexpectedly tumbles off the train and down an embankment. The story then transports us to Mégève, a renowned ski resort nestled in the French Alps, where Regina Lampert (Audrey Hepburn) finds herself dining alone at a table lavishly set for three. Oblivious to the imminent danger, she faces the unfriendly end of an automatic pistol, only to be sprayed with harmless water from a prank by the guilty-looking young boy, Jean-Louis Gaudet (Thomas Chelimsky). After the boy’s mother, Sylvie Gaudet (Dominique Minot), sends him away, Regina confides her intention to divorce her husband, Charles.
Sylvie, with a modern attitude, suggests indulging in affairs using Charles' wealth, but Regina is not swayed. Their conversation is interrupted by the suave Peter Joshua (Cary Grant), who claims that Jean-Louis was targeting Baron Rothschild with snowballs. Flirting ensues, and they agree to meet again in Paris. Upon returning home, Regina is shocked to find her apartment stripped bare, devoid of all belongings, and even devoid of her maid. Accosted by Inspector Edouard Grandpierre (Jacques Marin), Regina is taken to the Paris Morgue, where she identifies the dead man as her husband.
Inspector Grandpierre informs her that Charles, also known as Charles Voss in CIA circles, was found dead with a one-way ticket to Venezuela in his possession and that he had liquidated their apartment’s assets mere days before his demise for a whopping $250,000. However, the authorities suspect the money is missing. Grandpierre presents Regina with the meager belongings of Charles, including a wallet with a paltry 4,000 francs, the last appointment noted, and puzzlingly, four different passports under various aliases—only one of which Regina recognizes.
Later, at Charles' funeral, she is joined by Sylvie and Inspector Grandpierre. Their quiet ceremony is disrupted by the entrance of three shady characters: Leopold W. Gideon (Ned Glass), Tex Panthollow (James Coburn), and Herman Scobie (George Kennedy), who each represent a different aspect of Charles’ checkered past. Afterward, Hamilton Bartholomew (Walter Matthau), the CIA station chief, reveals to her that the three men were once soldiers alongside her husband and pleads with Regina to recover the stolen money or risk danger to her life.
As she sifts through the revelations, she meets "Peter Joshua" again at a café, but their lighthearted encounter soon takes a dark turn when threats emerge from Gideon and Tex demanding the money. Thanks to Peter, Regina narrowly escapes a deadly encounter with Scobie, who invades her hotel room. Peter's resilience shows as he chases the elusive Scobie, leading to a confrontation filled with suspense and unexpected revelations about his identity as "Dyle."
As danger builds, so does the intrigue, weaving tales of betrayal involving past military operations that left scars on all involved. Regina unravels a conspiracy rooted in World War II, where her husband and his cohorts once buried a fortune in gold. As she navigates this web of deceit with the enigmatic “Dyle”—who turns out to have been named Alexander—their connection deepens amid chaos.
However, the deadly stakes rise when characters are knocked off one by one, and the story crescendos to a confrontation at the Paris Opera House, where the truth about Charles, Carson Dyle, and a treasure hunt unfolds in a flurry of action and revelation.****
Through it all, Regina discovers more than just the truth about her husband; she finds love amidst peril, as "Brian Cruikshank," also known as "Dyle," captures her heart while ensuring her safety in a tumultuous world of espionage. In a heartfelt conclusion, Regina's commitment to pursuing what’s right leads her to deliver the riches to the American authorities, ultimately transforming her life in ways she never anticipated.
