Detective Allan Pinkerton, working for the Union, becomes obsessed with Southern socialite Rose O'Neal Greenhow, a spy for the Confederacy.

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.

A Pinkerton agent masquerades as a criminal in order to infiltrate a gang of counterfeiters that is using wealthy widow Lucy Randall as a front. Arriving at the gang's hideout the Dawson ranch, Red discovers that the counterfeiting ring is headed by Mrs. Randall's attorney J. Richard Spencer and Dawson himself.