The first U.S. spaceship to Venus crash-lands off the coast of Sicily on its return trip. A dangerous, lizard-like creature comes with it and quickly grows gigantic.

Global panic ensues when it is revealed that a mysterious UFO is actually a giant bird that flies at supersonic speed and has no regard for life or architecture.

A Giant Octopus, whose feeding habits have been affected by radiation from H-Bomb tests, rises from the Mindanao Deep to terrorize the California Coast.

Members of a joint Japanese-Rolisican expedition go to Infant Island, the scene of H-Bomb testing by the Rolisican government, and find that the heavily radiated island still holds life; two beautiful young women, the Shôbijin, only a foot high and singing guardians of Mothra, a sacred egg. Nelson, one of the Rosilican members, returns to the island to kidnap the twins and plans to exhibit them around the world. The egg hatches a gigantic insect larva that crawls into the sea. When the larva, now grown even more gigantic, reaches Tokyo, it wreaks havoc before it begins to spin a cocoon. Rolisican and Japanese troops attack it but their atomic-ray weapons only speed the metamorphosis of the larva into an adult moth of colossal size, impervious to all their weapons.