The Pony Express is finished as the Post Office plans to award the mail contract to a stage line. Bill and his father put in a bid for the mail, however there are three bids close together. The officials will run a race to pick the winner, and the Banton Brothers sabotage Bill's stage. Mary still believes in Bill until they try to get rid of him by holding up the regular stage with his well-known horse. Bill needs proof to clear himself and expose the bad guys.

"THE MAIL MUST GO THROUGH!"