Nuclear testing has triggered the sudden evolution of the Fumoon, a diminutive yet highly intelligent humanoid species inhabiting a small island, who are discovered by Dr. Yamadano. Aside from a handful of witnesses—namely detective Shinsaku Ban, the young men Rock and Kenichi, and Kenichi’s sister Pichi (Pinoko)—no one believes him. The Fumoon are abducting animals from across the globe to accompany them as they evacuate Earth using their spaceships, knowing that the planet is destined to be destroyed soon by a cloud of black gas resulting from a stellar explosion. Although the Fumoon plan to leave humanity behind, one Fumoon named Rokoko, who befriends Kenichi, attempts to assist Dr. Yamadano and the others in building a spaceship to enable a few humans to escape, with the aid of Dr. Ochanomizu and Dr. Frankenstein.