20 years ago, 3 men robbed a stage and hid $30,000. They were caught and sent to prison by Marshal Steve Autry. 20 years later, the men bust out of prison and return to the ghost town where they stashed their treasure searching. Steve's grandson picks up where Steve left off to foil the plans of the outlaws.

While trailing Forest Ranger Charles Carter, who is suspected of permitting lumber man Henry Mitchell to cut restricted timber, Gene fires at a dangerous mountain lion and apparently kills Carter. Actually, Bill Wright, Mitchell's associate, killed Carter because the ranger had discovered tussock moth infestation in the forest, and if the infestation was not reported, the trees would die and have to be cut, thereby profiting Mitchell and Wright. In order to compensate the best he can, Gene sells his sportsman's camp and gives the money to Carter's daughter Helen . En route to Texas, Gene discovers the infestation and is assigned by the Forest Department to supervise the program of spraying the area with DDT from the air. After the first day of spraying, the DDT is blamed by furious stock men for the many animals found dead of poisoning.