Former policeman Jay McGraw's job as a messenger for Wells Fargo takes him east on the San Francisco to Chicago run of the Central Pacific. While often routine and boring, guarding the famous Wells Fargo treasure box is a steady job. Rarely does he envy his close friends who still walk a beat in Chinatown.

But trouble soon comes his way. Not long into the run, a gang of masked bandits blow up a key bridge on the trail. Jay knows they are after his cargo, even though the train carries other valuable freight. If Wells Fargo loses their heavily insured shipment, Jay will lose his job. However, escaping from the heavily armed, very persistent riders seems impossible.

A last-ditch escape effort sees Jay fleeing the bandits by hot-air balloon, only to land in the midst of a deadly range war between cattlemen and Basque sheepherders deep in the Wyoming territory. Despite Jay's remote location, the bandits continue their dogged pursuit of him, and seem willing to risk anything to steal the precious lockbox.