Without warning, an alien spaceship attacks a Japanese moon base. Back on Earth, young Kenichi (Kenny in the English dubbed version) Ishikawa; his father, Dr. Yosuke (Henry in the English dubbed version) Ishikawa; his friend Helen Wallace; and her father, Dr. Tom Wallace, witness the spaceship descending into the ocean. They go to investigate, but are soon captured by a teleportation beam that brings them aboard the spaceship. Inside the spaceship, a human-looking woman appears to them and reveals that she is of an alien race called Zigrans. By way of demonstrating Zigran technological prowess, she creates a gigantic earthquake that wreaks havoc in Japan. She had previously caused two other earthquakes, one in Peru and the other in Arabia (in the English dubbed version, it mentions instead the Indian Ocean). She then tells her prisoners of the planet Zigra's history and its great scientific advances which, unfortunately, have resulted in its destruction; but in searching for a new home, Zigra has found Earth. The woman contacts authorities on Earth and orders them to surrender, or she will kill her prisoners. Tom declares that the Zigran woman is insane and, in anger, she sends the two men into a hypnotic trance. Kenichi and Helen take action, successfully using the ship's control console to escape with their fathers. Enraged, Zigra orders the woman to go to Earth and kill the children. She says it would be simpler to kill all the people of Japan, but Zigra tells her that humans must be preserved so they can be used for food. Now, Gamera, intent on discovering the identity of the alien interloper, flies in to save the day and rescues the children and their fathers. The U.N. authorities, after questioning Kenichi and Helen, resolve to attack Zigra. The Defense Force jets scramble, but the Zigran spaceship makes short work of them with its powerful lasers. The alien woman arrives on earth, disguised as a normal human, and begins her search for Kenichi and Helen. She h