As alien invaders plot to conquer the Earth, two Boy Scouts steal a mini-submarine and discover Gamera in their midst. Transported to the alien's spaceship, the Scouts are menaced by the evil inhabitants, including Viras, a squid-like monster that grows to colossal size to battle Gamera.

As a massive alien craft heads to Earth to do evil, three good and powerful superwomen befriend a young boy who has a special connection to Gamera, and old foes return to do battle one more time.

An alien woman from the planet Zigra and her spaceship creates a series of earthquakes around the globe. Two children at a marine park are caught in the crossfire as Gamera must combat the monster Zigra to save the earth.