Regina "Reggie" Lampert (Audrey Hepburn), tells her friend Sylvie Gaudel (Dominique Minot) while on a skiing holiday that she has decided to divorce her husband Charles. She then meets a charming American stranger, Peter Joshua (Cary Grant). On her return to Paris, she finds her apartment is completely empty and police inspector Edouard Grandpierre (Jacques Marin) notifies her that Charles has been murdered while leaving Paris. Reggie is given her husband's travel bag, containing a letter addressed to her, a ticket to Venezuela, passports in multiple names and other items. At the funeral, three odd characters show up to view the body.Reggie is summoned to meet CIA administrator Hamilton Bartholomew (Walter Matthau) at the U.S. Embassy. She learns that the three men are Tex Panthollow (James Coburn), Herman Scobie (George Kennedy), and Leopold W. Gideon (Ned Glass), the three survivors of a World War II OSS operation. Together with Charles and a fifth man, Carson Dyle, they were to deliver $250,000 in gold to the French Resistance, but they stole it instead. Dyle was fatally wounded in a German ambush, and Charles double-crossed the others and took all the gold. The three men want the missing money, and the U.S. government wants it back. Bartholomew insists that Reggie has it, even if she does not know where it is.Peter tracks Reggie down and helps her move into a hotel. The three criminals separately threaten Reggie, each convinced that she knows where the money is. Scobie then shocks Reggie by claiming that Peter is in league with the trio, after which Peter confesses to her that he is really Carson Dyle's brother, Alexander, and is convinced that the others murdered Carson.As the hunt for the money continues, first Scobie is found murdered, then Gideon is killed in an elevator. Meanwhile, Reggie falls in love with Dyle, but gets yet another shock when she learns from Bartholomew that Carson Dyle had no brother. Confronted with this, Alexander now admits he is actually Adam Canfield, a professional thief. Although frustrated by his dishonesty, Reggie still finds herself trusting him.Reggie and Adam go to the location of Charles's last appointment and find an outdoor market. They also spot Tex there and Adam follows him. Seeing booths selling stamps to collectors, both realize separately that Charles must have purchased rare stamps and stuck them on an envelope in plain sight in his travel bag, but when they get to Reggie's hotel room the stamps are gone because Reggie had given them to Sylvie's boy, Jean-Louis (Thomas Chelimsky), for his collection. Reggie now also realizes the stamps' significance, so she, Sylvie, and Jean-Louis find the stamp trader, Mr. Felix (Paul Bonifas) who, recognizing the value of the stamps, returns them to Reggie.Reggie Lampert (Audrey Hepburn) hiding from the unmasked Carson Dyle.Back at the hotel, Reggie finds Tex murdered as well. While dying, he wrote the name "Dyle". Assuming that Alexander is the murderer after all, a frightened Reggie telephones Bartholomew, who arranges to meet her. When she leaves the hotel, Adam spots her and gives chase through the streets of Paris and the subway. At the rendezvous, Reggie is caught out in the open between the two men. Adam tells her that Bartholomew is really Carson Dyle, who was only wounded by the Germans. After another chase through an empty theater, Adam kills Dyle to save Reggie.Next day Reggie and Adam go to the embassy to turn over the stamps, but Adam refuses to accompany her further. Going in, Reggie is shocked to find that Adam is really Brian Cruikshank, the government official responsible for recovering stolen property. Now his true identity is revealed, he promises to marry her.The movie ends with a split-screen grid showing flashback shots of Brian's four identities, while Reggie says she hopes that they have lots of boys, so they can name them all after him.
Output: Question: Who double crossed Dyle and the others by taking the gold?, Answer: Charles