When local efforts to put gangsters in jail are ineffective, the Federal government has some success by charging criminals with evading taxes on their illegal earnings. Bill Bradford, a treasury agent posing as a newspaper reporter, is assigned to the case of gangster Alexander Carston. Bill is in love with Julie Gardner, Carston's bookkeeper. She informs him that Carston's books are kept in code and she is the only one who knows that code. After they witness the brutal murder of a man who crossed Carston, Bill begs Julie to quit her job, but she is afraid that Carston will never let her go because she knows so much. At Bill's suggestion, the district attorney pressures the murdered man's partner into testifying against Carston, but an informer reveals the plan to Carston and the witness is murdered. After a jury fails to convict Carston, Bill divulges his real identity to the district attorney, and they formulate a plan to photocopy Carston's books. For her own protection, they arrest Julie as a material witness. She decodes the books, but before she can testify, Carston has her kidnapped. Bill tricks Carston into taking him to the hideout where Julie is being held. The police follow, killing the gang and rescuing Bill and Julie. Julie's testimony sends Carston to Alcatraz, and she is free to marry Bill.