Madame Fauvel, wife of a Parisian banker, is being blackmailed by her cousin, de Clameran, who insists she provide him with jewels and money because he knows her daughter Madeline is not her natural child. Madeline plans to elope with Prosper Botomy, the cashier at her father's bank, because she is against the marriage her parents have arranged in order to save the bank. Fauvel fires Prosper because of his elopement plans, but the bank is robbed shortly thereafter. Both Prosper and Mme. Fauvel confess to the crime. Detective Gaston Le Coq does not believe either story until he hears that Madeline is actually de Clameran's daughter, which explains the blackmailing, and that he forced Mme. Fauvel to steal the combination and keys to the bank safe. Suspecting de Clameran of a jewel theft as well as the bank robbery, Le Coq sets him up by having thief and murderer Michele break into his rooms, and then sending in de Clameran and his partner, Lagors, five minutes later. As hoped, Michele kills the thieves and is killed himself by the gendarmes after attempting escape. Fauvel recovers the money from the bank robbery, and his bank is further fortified by credit from the United States. Madeline and Prosper are reunited.