Convicted counterfeiter Eugene Deane appears to be a model prisoner, but actually is still practicing his craft, concealing the plates he is engraving in a hollowed-out Bible. After assisting the visiting chaplain with church services, Deane hides some plates in the lining of the chaplain's bag. The chaplain is later called to the home of a sick woman, and while he is with her, the man of the house is joined by a gangster, who retrieves the plates from his bag. Counterfeit $10 bills soon begin to turn up at gambling establishments, drawing the attention of the Treasury Department's Secret Service branch in Washington, D.C. Agent John Riggs searches Deane's prison cell and discovers his tools, but Deane, who has just been told he has only a few months to live, refuses to cooperate. The Secret Service gets its first lead when a Los Angeles detective catches a pickpocket named Nimble Willie with counterfeit money. Willie points out the man he robbed to Riggs, who trails him to the cigar store where the counterfeit money is exchanged, and identifies the ring's courier as Bill Evans, a traveling salesman. After Evans is arrested with a suitcase full of counterfeit bills and released on bail, Riggs instructs him to call the exchange for his contact, Reggie, and arrange a meeting. When Evans shows up for his assignation, however, Reggie and his henchmen take him to the top of an office building and throw him out a window. Riggs breaks the news to Mrs. Evans and searches the dead man's room, where he finds the label of an exclusive Beverly Hills tailor in a suit jacket. After learning that the tailor had delivered several suits to Evans at a Los Angeles hotel, Riggs checks in under the name Nick Starnes and quickly establishes himself as a big spender. Riggs has two FBI agents inform hotel manager Nora Craig that one of her guests has passed a $50 bill traced to a recent armored car robbery in Boston. He then gives Nora an envelope to be stored in the hotel safe, and when she secretly opens the envelope, she finds a stack of bills whose series numbers match those on the FBI's list. Nora and Riggs become romantically involved, and he soon receives a call from Reggie, who meets with Riggs and agrees to sell him $500,000 in counterfeit bills for $100,000. Meanwhile, the gravely ill Deane is on a train to a federal hospital when he overpowers his guard and escapes. Back at the hotel, Reggie becomes suspicious when he intercepts a cryptic telegram from Riggs's supervisor, Hugh Pringle, and Riggs is held prisoner at the gang's hideout in an abandoned warehouse. Reg summons Nora, who turns out to be the head of the counterfeiting ring as well as Deane's daughter. After Deane dies, Riggs calls Pringle and arranges to pick up the money for his transaction with the counterfeiters at Union Station, but when they reach Angel's Flight, Reggie manages to escape the Secret Service agents who are tailing them. They return to the hideout, and Riggs sends one of Reggie's men to the corner deli for sandwiches, giving him a $10 bill on which he has written instructions to call the Secret Service immediately. Meanwhile, Nora finds a sketch in Deane's notebook identifying Riggs as a Secret Service agent, and she orders her men to abandon the warehouse. The deli owner calls the authorities, and the police arrive just as the counterfeiters are setting the warehouse on fire, with Riggs still inside. Nora tries to escape with the money, and Riggs pursues her to a river bridge. There Nora loses her balance and falls into the path of a speeding train.