When the Bureau of Investigation (so-called because Monogram didn't have J. Edgar's stamp of approval) learns that wealthy philanthropist Mrs. Crippen bosses the city's underworld, Federal Agent Tommy Thompson is detailed to uncover evidence that will convict her. Masquerading as a crook, Tommy is saved from jail by the Crippen machine, which is headed by Harker, Mrs. Crippen's lawyer and partner. Tommy joins the gang, wins the old lady's confidence and fall in love with her secretary, Milly, who is unaware of her employer's criminal activities. Mrs. Crippen is working to save her son John from the electric chair. Tommy brings John, who has escaped from the penitentiary, directly to Mrs. Crippen so she can be caught red-handed. Tipped off that the police are closing in, she leaves for her hideout with Tommy, John, Milly (who she has kidnapped) and two henchmen. Harker has discovered Tommy's true identity and relays the information to the gang.