In 1869, the United States begins a railroad mail service to the West Coast which proves highly tempting to train robbers, in particular an organized gang with one of the mail's supposed guardians in their pay. Prizefighter Steve Davis, a former army intelligence man, is hired to track down the gang and save the Territorial Mail Service. Steve goes undercover in territorial prison, learns Morse Code from a fellow prisoner, breaks jail, infiltrates the gang...and finds time to romance dance-hall singer Mary, who proves to have hidden depths...