Based on the comic book character "Thun'Da, King of the Congo," a Tarzan imitator, whose only comic of any value is the first one rendered entirely by cult artist Frank Frazetta, this was Columbia's 48th serial and the seventh and last serial starring Buster Crabbe. Crabbe plays U.S.A.F. Captain Roger Drum who shoots down an unidentified plane whose pilot was bound for Africa to deliver a message to a subversive group. Drum takes his place, makes the flight and crashes in the jungle. The rock people, led by Princess Pha, rescue him and take him to their temple. The subversives, led by Boris, appear and Drum rings a temple gong in alarm, and its sound crumbles the walls, burying him in debris at the end of Chapter One, "Mission of Menace." Chapter Two, "Red Shadows in the Jungle" finds Drum being proclaimed Thunda, King of the Congo, by the natives but is still mistrusted by Princess Phi and her assistant Nahee, still miffed that he rang the wrong gong. This goes on for 15 chapters before Thundra reunites the Rock and Cave People and clears the jungle of all the villains with Russian names.