 John Robie is a one-time cat burglar, now reformed and living a blameless life in a plush villa. When a fresh set of burglaries rocks the Riviera all bearing the hallmark of Robie s own robberies, he is the natural suspect. Robie sets out to catch the new burglar himself, mainly to prove his innocence. He is aided by an American heiress, who initially is convinced that he is actually guilty. The title of the movie is derived from the proverb "Set a thief to catch a thief"