An atomic explosion awakens Gammera, a giant fire breathing turtle monster from his millions of years of hibernation.

An expedition goes out to a remote island to find a priceless opal. This opal happens to be the egg of the powerful Barugon, a huge lizard-like monster that can freeze foes with its long tongue or disintegrate them with its devastating rainbow ray. When Gammera begins to fight Barugon, several plans begin to stop both monsters and keep the damage of Japan at a minimum.

Aliens begin a plan to take over the Earth by using the monster Gammera, now under their mind control, to do their bidding. When 2 boys thwart the aliens and reverse its controls, the aliens combine and grow to giant size to fight Gammera.

Two children get into a flying saucer and end up on the other side of the sun where they dream of donuts and milk and a hero turtle. The women there want to eat their brains.