“Gamera burns the streets of Osaka in an instant! Barugon freezes Osaka Castle with a single gust! An underwater clash at Lake Biwa!”

Gamera escapes from his rocket enclosure and makes his way back to Earth as a giant opal from New Guinea is brought back to Japan. The opal is discovered to have been an egg that births a new monster called Barugon. The creature attacks the city of Osaka by emitting a destructive rainbow ray from his back, along with a freezing spray capable of incapacitating Gamera.