The man who accepts the job at the monster-themed park is named Gengo Kotaka. He soon discovers that the park is a front for the alien race known as the M Space Hunter Nebula Aliens, who are using it as a base for their invasion of Earth. Gengo manages to make contact with Godzilla and Anguirus, who are living on Monster Island at the time.
The aliens unleash their two monsters, Ghidorah and Gigan, on the city to begin their attack. Godzilla and Anguirus arrive on the scene to fend off the attackers, but they quickly find themselves outmatched. Gigan has a buzzsaw in place of one of his hands, making him a particularly formidable foe.
Meanwhile, Gengo joins forces with a young woman named Tomoko, who has her own reasons for wanting to stop the alien invasion. Together, they work to uncover the aliens' plans and find a way to stop them.
In the end, Godzilla and Anguirus manage to defeat Ghidorah and Gigan, with some help from a newly-awakened King Seesar. The aliens are forced to retreat, and Gengo and Tomoko are hailed as heroes for their efforts in saving the planet.
