Shaken by repeated earthquakes, Industria will soon be overtaken by water. While its inhabitants are diligently preparing to flee from the isle, they are unexpectedly ambushed by Lepka, an enemy whom they had believed to be dead. Lepka has been hiding underground, waiting for an opportunity to hijack Industria's solar energy and fuel Gigant—a warplane capable of mass destruction which he aims to use to take over the world.

Fortunately, Lana and Monsley quickly realize Lepka's sinister plans and escape from Industria to alert Conan and his group, who are arranging a ship for the island's evacuation. Upon hearing the disturbing news, Conan, alongside his spirited friends Dyce and Jimsy, readily embarks on a perilous mission to bring down the menacing Gigant.