Reggie Lambert (Audrey Hepburn) returns home after a skiing trip to discover that her husband has died. At the funeral she finds out from CIA agent Hamilton Bartholomew (Walter Matthau) that her husband was involved in the theft of a quarter of a million dollars during World War Two. The charming Peter Joshua (Cary Grant) offers his help, but as the number of dead bodies increases so do Peter's aliases, and Reggie becomes uncertain whether or not she can trust him.

In Second World War France, German Colonel von Waldheim (Paul Scofield) orders the railway transfer of priceless works of art from the Jeu de Paume museum in Paris to the Fatherland. The French Resistance are determined to stop the cargo ever reaching Germany, and enrol railway inspector Labiche (Burt Lancaster) to help them in their cause. Franklin Coen and Frank Davis's script was nominated for an Oscar.