Fujiko is taken hostage in exchange for the world's largest ruby, which Arsène Lupin III recently acquired from the royal house of India. The demand comes from Fantomas Mark III, the grandson of the legendary European criminal mastermind Fantomas. He intends to use the ruby as the oscillation unit of a laser satellite, with which he will melt the Antarctic ice and thus flood the world's cities, enabling him to achieve world domination. However, Lupin is outraged that Fantomas would use his ruby and Fujiko for something like that, and sets out to stop him. But will he figure out how to swim in space?
—Tenchi