An IRS agent and his girl-friend bookkeeper for a gangster are able to get the gangster convicted of income tax evasion after other trials failed.
The Internal Revenue Service (IRS) sends agent Bill Bradford (George Brent) after Nick Carston (Ricardo Cortez), who was just acquitted by a jury for bribery. Carston has Julie Gardner (Bette Davis) check the gambling contracts of Alec Armitage (Robert Strange), and $30,000 is missing. Bill asks Julie to dine. Alec asks Jake Andrews (Jack La Rue) for help, and Andrews tells him to call the District Attorney. Carston finds out and sends Joe (J. Carrol Naish). As police are taking Alec down the steps, he and four others are killed in a drive-by shooting. Bill reports the story. Carston tells Joe that he killed too many. Joe walks out, and Carston orders him killed too.
The District Attorney (Henry O'Neill) tells Andrews they have evidence on him and asks for information on Carston. Andrews talks; but the D. A.'s file clerk Williams (Paul Guilfoyle) goes to Carston and gets $10,000 for a document, Julie bringing in the cash. Carston warns Julie about seeing Bill. Carston tells Bill that he expects to be arrested and sprung. Bill wants to marry Julie; but she's afraid to leave Carston; only she knows his bookkeeping code. Carston is tried for the massacre; but the witness is killed, and a document was "lost."
Bill shows the D. A. he is an IRS agent, and he tells Julie too, asking for Carston's books. Bill calls Carston to warn him the feds are coming for his books, then sends his men. Carston gives the books to Julie to hide. While the men search Carston's office, Bill gets the books from Julie and has them copied. The D. A. questions Carston and his lawyer (William B. Davidson). Julie is arrested for safekeeping, and she helps Bill understand the books. Julie tells the D. A. that his file clerk Williams was paid for informing Carston. Carston is tried for income tax evasion. On her way to court Julie is abducted by two of Carston's men. Bill has Williams inform Carston about him; then he goes to Carston. Carston has Rich (Joe Sawyer) take Bill to his castle, and the police follow. Bill is tied up next to Julie; but the police close in and rescue them. Carston calls and talks to Bill. In court Julie testifies about the code. Carston pulls a gun, but Bill shoots it out of his hand. Carston is convicted and sent to Alcatraz. Bill takes time off to marry Julie.
Al Capone was convicted of tax evasion in 1931, and this tactic was used against other underworld leaders as well. This story adds romance with the gangster's bookkeeper, allowing the audience to root for the lovers and against the crime boss to a satisfactory conclusion of each case. No one seems to question the ethics of a government agent posing as a reporter.