Jean, Nadia, and King are rescued by an American battleship in pursuit of sea monsters, who have apparently been responsible for sinking ships. That night, the battleship is attacked, and Jean, Nadia, and King are thrown overboard....

In a surprising turn of events, Grandis and her boys join forces with Jean to save Nadia, Marie, and King from Gargoyle. Their escape attempt nearly backfires, until the Nautilus shows up to save them....

In pursuit of Gargoyle, the Nautilus becomes trapped in a dangerous underwater mine field. Sanson and Hanson jump aboard the Gratan to clear the mines before they detonate. Jean sneaks on to help the two men....

Captain Nemo's vessel falls into yet another deadly trap set by Gargoyle--one which involves the Garfish and a surprise attack from American battleships. The subsequent damage costs the lives of several sailors--including a friendly young engineer named Ensign Fait. Jean, who had become friends with Fait, is horrified and devastated to witness someone being killed by the technology he had so strongly idealized with.

Jean is tired of being treated like a child by the Nautilus crew. Hoping to cheer him up, Nadia suggests Jean to build another aircraft. Inspired, he sets off to do just that. At first he is determined to construct the new helicopter by himself, but then realizes he still needs the support of some grown-ups. With Hanson's help, Jean completes the craft and takes Nadia on a very delightful test flight. While airborne, Jean promises that he will one day take Nadia to Africa....

The Nautilus is ensnared by Gargoyle's super powerful SeaNet magnet. In the fight that follows, Grandis, Sanson and Hanson escape on the Gratan (to help free Nemo and the others from Gargoyle's battleship). The battle culminates with the badly damaged Nautilus plummeting into the sea....

A violent row between Sanson and Hanson turns into a race between two mechanical lions resembling King(!).

Gargoyle's battleships appear over Tartessos. To save Jean and the others, Nadia surrenders herself... but not before Jean swears to save her. Forced to flee from Gargoyle's battleships, our pals run into Captain Nemo and his crew, who have survived... and now operate a superpowerful battleship called the New Nautilus.

Gargoyle takes Nadia before the puppet leader of Neo-Atlantis, Emperor Neo, who reveals that he has a strong connection with both Nadia and Nemo. Eight time zones away, Nemo and the others plan to fight Gargoyle in a final duel. Throughout, both Jean and Nadia learn about the origins of the Atlanteans.