John Robie is suspected of a new rash of gem thefts in the luxury hotels of the French Riviera, and he must set out to clear himself. Meeting pampered heiress Frances (Grace Kelly), he sees a chance to bait the mysterious thief with her mother's (Jessie Royce Landis) fabulous jewels. His plan backfires, however, but Frances, who believes him guilty, proves her love by helping him escape.