As part of a plan by Buffalo Bill, Jr., Tony Castelar goes undercover, posing as a silver smuggler, in order to find the source of Mexican silver bars being brought illegally across the border.; In order to force a competitor, the Blue River Bank, out of business, Ned Ranton, owner of the Granite City Bank, orders his men to rob a shipment of cash intended for the Blue River Bank. He stores the extra cash in his bank's vault, but it draws the attention of his (honest) cashier, Henry Cameron. Bill has to figure out a way to prove the extra money came from the stolen shipment.