When a giant stone statue on Wester Island is disturbed, the legendary monster Jiger appears and heads for Japan. Gamera tries to stop this new rival, only to be injured when Jiger lays eggs inside of him. As two boys in a submarine go on a dangerous quest inside of Gamera's body to save him, Jiger threatens the Expo '70 world's fair in Osaka.

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. The alien Zanon launches a battery of familiar foes against Gamera, who might have to give the ultimate sacrifice to defeat the alien invader.