In the darkness behind Jupiter there lurks a heretofore undiscovered planet, Planet X, boasting beings of superior intelligence. The Planet X-ers are forced to live underground because of the havoc wreaked on the surface by Ghidra, the three-headed monster. Once discovered by our astronauts, including the ultra-hip Nick Adams (spouting such phrases as "That's right, baby!" with innocent conviction), the Planet X-ers propose that they transport Godzilla and Rodan from Earth to their planet to help rid them of the Ghidra menace. Only, as it turns out, they have a dastardly plan to use the bipedal behemoth and his flighty friend to conquer the Earth, harnessing their destructive force with "magnetic waves."