Matthew Versigny, the head of an American diamond concern, travels abroad with his sister Marguerite to learn the source of some imitation stones which are so perfect that even his company has purchased them. In Paris, they join forces with Paul Bernac, a special agent of the French Secret Service, and Andre Zarnoff, the chemist who invented the formula for the fake stones. The trail brings them into contact with Arthur Graves, the master mind of the counterfeiting ring, who determines to eliminate Versigny. After kidnapping his adversary, Graves employs the Baron de Lambri, Versigny's former manager, to steal the secret formula from Versigny's safe, thus making it appear as if Versigny had decamped with his company's papers. Versigny finally escapes and, with the aid of Bernac and Marguerite, tracks Graves down and captures the villains.