After surviving Godzilla's attack on San Francisco, Cate is shaken yet again by a shocking secret. Amid monstrous threats, she embarks on a globetrotting adventure to learn the truth about her family—and the mysterious organization known as Monarch.

Brought together by a mysterious song, a grad student and an engineer lead the fight against an unimaginable force that may spell doom for the world.

Zone Fighter, known in Japan as Ryūsei Ningen Zone, is a tokusatsu science fiction superhero television series. Produced by Toho Company Ltd., the show aired on Nippon Television from April 2 to September 24, 1973, with a total of 26 episodes, it was cancelled due to the oil crisis of 1973. This was Toho's answer to not only the popular Ultra Series, but the Henshin Hero phenomenon started by shows like Kamen Rider and Android Kikaider. The previous year, Toho had just made their successful first superhero show, Rainbowman. The series was also notable for its guest appearance by Toho's own Godzilla, as well as two other Toho monsters, King Ghidorah and Gigan. Supplementary materials published by Toho have confirmed Zone Fighter to be part of the Showa-era Godzilla series, taking place in between Godzilla vs. Megalon and Godzilla vs. Mechagodzilla.