Crime boss Duke Bates (George Sanders), a dead ringer for crime fighter Simon Templar (also Sanders), also known as the Saint, ships an Egyptian mummy to archeology professor Horatio Bitts (Thomas W. Ross) in Philadelphia. Templar happens to be on the scene visiting Bitts, his old friend and teacher, and is suspected of smuggling diamonds found in the mummy. Templar is forced to clear himself from suspicion while pursuing the real culprit, who he realizes is his double, Bates.