Guy Palisse, space-explorer, returned to Earth in the Bolton Flying Cube after ten years on the Sun's first planet, Mercury. He returned to report that he had warded off war between the two worlds, and to wed before an admiring planet his beautiful fiancée, Tama, winged princess of Mercury's Light Country. But following on Palisse's orbit was a new wave of terror, as barbarian hordes from Mercury's Cold Country descended to launch their conquest of Earth. And Palisse's triumph turned to near disaster as the frenzied Mercurians plotted to kidnap Tama and bring the Earth to ruin.