Synopsis by Hans J. Wollstein
The sudden arrival at Tonga's (Clarence Lung) village of Marjorie Elmore (Jane Adams) gives Tal Shan (Keye Luke) the opportunity to free Rod Stanton (Russell Hayden) from the guillotine just as the sun's rays cut the final rope that holds the blade in place. Although Indra (Helen Bennett), the ruler of Pendrang, has decided to throw in her lot with the Peace Foundation, she can do nothing to stop Malborn (John Mylong) and Sir Eric (Lionel Atwill) from getting to Tonga. Finally in possession of both the plaque and Tonga, the megalomaniacal Sir Eric rids himself of a dangerous rival by having Malborn shot. Tonga, who begins to suspect that he has been tricked, suffers the same fate after revealing that the meteorium is to be found at the Cave of the Hidden Sun. Sir Eric recovers a chest containing the radio active material he needs to dominate the world but is trailed by Rod and Tal. In the ensuing chase, Tal's automobile plunges into a deep ravine.