Gene (Gene Autry) is a singing cowboy happily running a radio station that happens to be located just above a mystical subterranean city. Conniving scientists discover the city and its rich deposits of radium ore and make plans to invade the underground world -- but first they must knock Gene out of the picture. The cowboy is not easily discouraged, however, and he enters the depths with his young sidekicks Frankie (Frankie Darro) and Betsy (Betsy King Ross) in order to set things right.