Regina Lambert (Audrey Hepburn) returns to Paris from a holiday in Switzerland to find that her husband, Charles, has been murdered and her house ransacked. She is later told by a CIA agent that her husband was involved in robbing $250,000 of gold from the U.S. government during World War II, and the government wants it back. Later that day she is visited by Peter Joshua (Cary Grant), whom she had met briefly whilst on holiday.

When her husband's ex-partners in crime, who were double-crossed by Charles, start harassing her about the missing money, Peter offers to help find it. Thus begins an elaborate charade in which nothing is what it seems to be...