Al Goddard (Alan Ladd), a detective who works for the United States Postal Inspection Service, is assigned to arrest two criminals who've allegedly murdered a U.S. postal detective.
Two newly-appointed postal inspectors, Frank Marshall and 'Slim" Hewitt, set out to track down the sender of a time-bomb to a U. S. Senator and, during their investigation, run across a hooded organization that is terrorizing an American city. They also meet Don Foster, who is loud in his condemnation of the terrorists, and his sister, Nancy, who fears for her brother's life.
Investigators set out to capture a gang of thieves transporting stolen cash through the U.S. mail.
Postal inspectors track down money stolen from a railroad car.
Postal Inspectors Carson and Underwood have been sent to investigate a series of robberies where both the driver and stagecoach disappear. They team up with Pinkerton agent Bennett who has found some of the stolen money in the possession of Stevens.
Postal inspectors investigate a con man who uses the identities of others to falsify credit card purchases. Stealing credit card offers from mail boxes, he obtains cards in others' names, makes many purchases until the card is maxed out, but is always careful to pay minimum balances. According to the story, it is possible for individuals such as this to run many credit cards at a time without being caught.