A moon base is destroyed by a spaceship from Zigra which is looking to take over the planet earth to use its oceans for its ocean-dwelling denizens. Gamera must once again come to the aid of the human race while all of Japan roots him on.

Unusual volcanic activity in Japan awakens Gyaos, a bloodthirsty flying monster with the power to slice things in half with an ultrasonic ray. While scientists and the military scramble to devise a way to stop this new threat, a young boy forms an alliance with Gamera; a monster no one else seems to trust.