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

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.

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.