An old fisherman brings Professor Yano a strange creature resembling a tadpole and casually complains that his catch has dropped sharply. Soon, the TV news shows something gigantic breaking a ship in half, and the professor’s son Ken finds a resemblance to the fisherman’s “tadpole.” The professor and his son set out to explore the coast. They discover a giant “tadpole.” Ken names the creature Hedora. Further study reveals that Hedora feeds on pollution from the bay, and small Hedora tadpoles can form into a giant Hedora, which can take any shape and even fly. Soon, the giant Hedora appears in Sagami Bay. The monster climbs onto the pipes of a local factory and, like a heavy smoker, inhales smoke from them. Godzilla challenges the new monster. People begin to die in the battle between the two titans. Who will stop the monster?