Treasury agent Dave Elliot (Donald Cook) dedicates himself to smashing a crime syndicate, especially after his best friend is killed by the mob. This requires Elliot to go undercover, posing as a criminal. He gains the confidence of sadistic mob gunman Lefty (J. Carroll Naish), and it's nip-and-tuck from then on until the identity of the mysterious Mister Big is revealed. Evalyn Knapp is excellent as glib-tongued mob bookkeeper Maxine, and Warren Hymer is equally good as a stupid numbers runner. Confidential can be seen as a Mascot Pictures pocket version of Warner Bros.' Special Agent, which in turn was inspired by the tax-evasion downfall of Al Capone.