When the ancient continent of Mu sank beneath the ocean, some of its inhabitant survived in caverns beneath the sea. Cowboy singer Gene Autry stumbles upon the civilization, now buried beneath his own Radio Ranch. The Muranians have developed technology and weaponry such as television and ray guns. Their rich supply of radium draws unscrupulous speculators from the surface. The peaceful civilization of the Muranians is corrupted by the greed from above, and it becomes Autry’s task to prevent all-out war, ideally without disrupting his regular radio show.
CHAP. 1 SINGING COWBOY: Professor Beetson and his associates arrive at Gene’s Radio Ranch looking for a buried city and a fortune in radium. When Gene helps them look for the secret entrance to Murania located 25,000 feet below Radio Ranch, the Muranian Queen sends her men to kill Gene. CHAP. 2 THUNDER RIDERS: Wanting everyone off Radio Ranch so they can investigate in private, Beetson frames Gene for murder. CHAP. 3 LIGHTNING CHAMBER: In Murania Lord Argo is planning a revolution while on the surface Gene flees from the Sheriff in a car without brakes. CHAP. 4 PHANTOM BRAODCAST: Still fleeing from the Sheriff Gene must make his radio broadcast or lose his contract and the ranch. CHAP. 5 BENEATH THE EARTH: Switching clothes with a Muranian, Gene is taken to the underground empire where the Queen sentences him to die. CHAP. 6 DISASTER FROM THE SKY: Gene tries to stop the radium bomb the Queen has sent to kill the riders on the surface. CHAP. 7 FROM DEATH TO LIFE: Declared dead the Queen sends Gene to the revival chamber so she can learn the name of the traitor that previously released him. CHAP. 8 JAWS OF JEOPARDY: Reaching the surface Gene takes Beetson’s airplane but the Queen sends a ray that kills the engine and the plane crashes. CHAP. 9: PRISONERS OF THE RAY: Frankie and Betsy are taken to Murania. Escaping their captors they throw the switch that will enable Gene to find the secret surface entrance only to be apparently electrocuted. CHAP. 10 REBELLION: Gene tells the Queen that Argo is the traitor and learning of this, Argo starts the revolution. CHAP. 11 QUEEN IN CHAINS: Argo takes over control Murania and sentences the Queen to death. CHAP. 12 END OF MURANIA: Gene saves the Queen and locks Argo and his men in the room with the death ray which gets out of control. With the end of Murania imminent the Queen refuses to leave. Gene and the others reach the surface where Gene must still face the murder charge.