When he is chased out of Texas for killing the leader of a band of desperadoes, Steve Jordan seeks refuge in a shack owned by his old friend and teacher Professor Arkansas Higgins. After Steve explains that he was unjustly charged with murder for shooting the man in self- defense, the professor helps him elude his pursuers and escape. Along the trail Steve spies a riderless horse. When he approaches the animal, however, he notices a man with a broken leg lying alongside the road. Steve sets the broken leg, and in gratitude, the man, Alexander Morton, gives Steve his horse. Continuing down the trail, Steve meets his old friend Ernie Tubbs, who persuades him to accompany him to St. Joe, where he plans to seek employment with the Pony Express. In St. Joe, Steve discovers that Morton is the owner of the Express. Morton hires Steve and his friend, but when Capt. Amos Karnes, a strict military disciplinarian, is put in charge of the operation, the men rebel. Alice, Morton's daughter, convinces the men not to quit, however, and they are assigned to a deserted Pony Express outpost. After renegade Indians capture their supply wagon and kill Blackburn, the man assigned to guard it, Johnson, the white leader of the renegades, assumes Blackburn's identity. Upon returning to the post, Blackburn approaches Morton and tells him that a group of gamblers is willing to pay him $10,000 if the Express fails. When Morton refuses his offer, Blackburn signals the Indians to kill him. Concerned about Morton's prolonged absence, Steve goes to look for him and discovers his body. When he questions Blackburn about Morton's death, Blackburn repeats his offer to Steve, and Steve accuses him of murder and orders his arrest. Blackburn escapes, however, and launches a series of Indian raids on Express outposts. Dedicating himself to saving the Express, Steve does the work of three riders, but when he returns to the outpost, Karnes arrests him for the Texas murder. When the Indians kidnap Karnes and hold him for ransom, Steve convinces the captain's aide that Blackburn is involved in a plot to defeat the Pony Express and persuades the aide to release him. Organizing a raid on the Indian village, Steve and his men free Karnes, and the Indians, feeling betrayed, kill Blackburn. Upon returning to the outpost, Steve is exonerated of all murder charges when it is discovered that the man he allegedly killed is alive and serving a jail term for embezzlement. In recognition of Steve's efforts to help build the Pony Express, Karnes rewards Steve with a lifetime job.