The FBI files are filled with many lurid crime stories. One case in particular baffles FBI Inspector Briggs (Lloyd Nolan). It's the murders of a housewife and a band guard, with no connection between the victims - except the murder weapon. Determined to solve the case, Briggs sends his best agent undercover to penetrate the inner circle of a notorious gang run by up-and-coming crime boss Stiles, played by Richard Widmark in one of his most chilling performances. Everything goes according to plan, until an informant tips off Stiles.

The murder of two innocent people leads to an F.B.I. investigation which uncovers the head of the city Mob. Based on an actual case.