At a state game preserve for animals, two escaped convicts, oil engineer Del Roberts and Bob Oliver, kill a fawn for food. Meanwhile, from their lookout station at Susanna Pass, Foy Willing and his men spot the convicts' campfire and sound the alarm. While game warden Roy Rogers organizes the fire fighters, Roberts stabs Oliver and escapes in a wagon. After the fire is put out, Roy notices the wagon tracks and then finds the deserted wagon, which he recognizes as belonging to the state penitentiary. In town, meanwhile, Roberts tells newspaper editor Martin Masters that now that Martin's nephew, Oliver, is dead, Martin will need a new partner. When Martin agrees, Roberts shows him a map revealing rich oil deposits underneath a fish hatchery lake owned by Martin's brother Russell. Meanwhile, Roy tells cook Carlos Mendoza that Sheriff Murphy has asked Roy to take over his duties while he recovers from a broken leg. Later, Roy and Carlos see Kay "Doc" Parker fishing without a license, she explains that she is an ichthyologist who is working for Russell. To determine seismologically the exact location of the oil, Roberts, meanwhile, detonates a bomb underneath the lake. Roy and his men feel the blast and chase Roberts and Martin, who escape in their truck. The saboteurs dive out of the truck before it sinks into the lake and explodes, killing most of Russell's fish. Although he is worried that he may lose his lucrative state contract, Russell rejects Martin's suggestion that he sell his hatchery. When Martin explains that Russell has refused to sell, Roberts suggests murder so that he can inherit the land. After Martin's henchman, Vince, harasses Carlos' daughter Rita, Roy punches him. Knowing that Russell cannot swim, Martin waits until Russell takes his boat out onto the lake and blasts holes in it, causing Russell to drown. Despite the fact that Roy and his men recover the boat and find the bullet holes, a court inquiry finds Russell's death to be accident. When Russell's lawyer reveals that his will was altered just before the murder, leaving the hatchery to Doc, Roy accuses her of being involved in Russell's death. Doc's alibi, Walter P. Johnson, who is actually Roberts, refuses to vouch for her whereabouts, so Roy arrests her for murder while telling her that he knows that she is innocent. After Rita releases Doc from jail, they tell Roy about the oil deposits which they have just discovered. Having recovered from his stab wound, Oliver suddenly appears and takes Doc hostage at gunpoint. He insists that Roy accompany him to the lake, and there pulls his gun on Roberts. Roy chases Roberts to the hatchery, where he asks a bird named Jim to show him where Roberts is hiding. After Jim flutters over to Robert's hiding place and lands on his head, Roberts is arrested. The remaining outlaws are then arrested, and Doc decides to stay on at the fish hatchery.