Bizarre 1930s serial about a singing cowboy defending his radio ranch from evil robots and mad scientists from the subterranean empire Murania.

A gang of crooks led by the nefarious Prof. Beetson seeks a valuble radium deposit located beneath Radio Ranch, managed by popular country western radio star gene Autry. Autry must broadcast his radio program once a day to fulfill a clause in his lease and maintain conrol of Radio Ranch. Realizing that Autrys popularity draws a crowd to the ranch, Beetson attempts to eliminate Autry by murdering the singer's business partner (the father of autry's two young friends Frankie and Betsy Baxter) and framing autry for the killing.

Autry escapes custody in an effort to prove his innocence. Grankie and Betsy, loyal to Gene and knowing that he did not kill their father, aid him in his quest, along with a group of their friends who have formed a childrens club called the Thunder Riders, patterned after a mysterious group of masked horsmen (called the Thunder Riders) periodically seen in the area. Eventually, both Autry and Beetson discover that the real Thnder Riders come from an advanced, forgotten civilization called Murania, located 25,000 feet below Radio Ranch.

Autry is eventually imprisoned in the subterranean city, ruled by the haughty Tika. Young Frankie and Betsy, along with Autry's dim witted buddies Pete and Oscar, are also captured when they follow Gene into Murania. Although Gene manages to escape Queen Tika's clutches repeatedly so that he can return home and deliver his mandatory radio broadcasts, he and his friends are constantly threatened by Queen tika and the Muranians until Argo, a treacherous underling of the monarchs stages an armed revolt and overthrows her.

Gene and his friends escape from Murania just as a powerful death ray goes out of control, disintegrating the entire city and all its inhabitants. Safely returning to the surface, gene, Frankie, Betsy and the sheriff contrive to eavesdrop on Beetson as he discusses Murdering Frankie and Betsy's Dad. With this evidence, Gene is finally able to prove his innocence and clear his name, with beetson punished for his misdeeds.