A singing cowboy stumbles across an ancient underground civilization beneath his ranch.

The Baxters find Gene in time to save him; Argo orders the death of all surface people; battling, Gene arrives at where the Queen is being executed, but is knocked into the path of death-dealing rays.

Gene tries to stop the radium bomb sent by the Queen to kill the riders on the surface.

Gene is pulled to safety, and the Queen is rescued; the ray goes wild, destroying Murania; the Queen orders all to the surface, where everyone and the ranch are safe, while staying behind herself.

After defeating the guards, Gene reaches the surface and takes Beetson's airplane; the Queen kills the engine.