An underwater clash at Lake Biwa!
A meteor crashes into the rocket-ship in-prisoning Gamera. Hungry for energy, Gamera makes his way back to Japan. Meanwhile, an expedition to retrieve a giant opal results in disaster as the opal is revealed to be an egg. The egg spawns Barugon, an ancient reptilian monster that terrorized the natives of its island. Gamera and Barugon soon collide in a climatic battle.