The Phantom Empire is a 1935 American Western serial film directed by Otto Brower and B. Reeves Eason and starring Gene Autry, Frankie Darro, and Betsy King Ross. This 12-chapter Mascot Pictures serial combined the western, musical, and science fiction genres. This was Gene Autry's first starring role, playing himself as a singing cowboy.
Gene Autry is a singing cowboy who runs Radio Ranch, a dude ranch from which he makes a daily live radio broadcast at 2:00 pm. Gene has two kid sidekicks, Frankie Baxter (Frankie Darro) and Betsy Baxter (Betsy King Ross), who lead a club, the Junior Thunder Riders, in which the kids play at being armored knights of an unknown civilization, the mysterious Thunder Riders who make a sound like
thunder when they ride. The kids, dressing up in capes and water-bucket helmets, play at riding "To the rescue!" (their motto). A chance to become real heroes occurs when Betsy, Frankie, and Gene are kidnapped by the real Thunder Riders from the super-scientific underground empire of Murania, complete with towering buildings, robots, ray-guns, elevator tubes that extend miles from the surface, and the icy, blonde, evil Queen Tika. On the surface, criminals led by Professor Beetson plan to invade Murania and seize its radium wealth, while in Murania, a group of revolutionaries plots to overthrow Queen Tika.
The inhabitants of Murania are the lost tribe of Mu, who went underground in the last glacial period 100,000 years ago, and now live in a fantastically advanced city 25,000 feet below the surface. They cannot now breathe the air at ground level and must wear oxygen masks. (Surface dwellers have no trouble breathing Muranian air.) The Thunder Guard emerges to the surface world from a cave with a huge rock door that swings up like a garage door. Both Muranians and Professor Beetson want to get rid of Autry, so he loses his radio contract and Radio Ranch is vacated. (Source: wikipedia.org)