Japan is thrown into a panic after several ships explode and are sunk near Odo Island. An expedition to the island led by paleontologist Professor Kyohei Yemani soon discover something…

A 400-foot (122-meter) dinosaur-like beast, awoken from undersea hibernation off the Japanese coast by atomic-bomb testing, attacks Tokyo.

The aftermath of the Oxygen Destroyer brings forth Destoroyah, a beast intent on killing Godzilla, who is on the verge of a nuclear meltdown.