Jean, a 14-year-old orphan, sailing into Paris to help his uncle design an airplane for the Paris Exposition's flight competition meets a pretty young girl named Nadia and her pet lion cub, King. He ends up rescuing her from a woman named Grandis who is trying to get Nadia's jewel, the Blue Water. Nadia leaves the only home she ever knew - a circus - as Jean has offered to help her search for her place of origin, starting with the random choice of Africa...

Imprisoned by the wicked Gargoyle, Nadia is forced to admit that she gave her Blue Water to Jean before turning herself in (to save Marie and King from a horrible fate). As the search for Jean is on, the boy desperately tries to find her. Simultaneously, Grandis, Sanson, and Hanson, who have also been imprisoned by the soldiers, break out of their prison cell and attempt to escape. While Gargoyle tours Nadia around his base, he showcases Neo-Atlantis's secret weapon, a tower known as Babel with the power to obliterate an entire island!

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....

When the Nautilus docks on an island to reestablish supplies, Nadia bonds with Grandis when the latter tells her how the first man she fell in love with turned out to be a treacherous cad.

The victims of Gargoyle's latest attack are taken to the long-forgotten underworld of Atlantis to be buried. While there, Jean discovers that his father's ship was sunk by the Garfish. Nadia also learns that she must keep the Blue Water at all costs, no matter what pain or damage it may cause.

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....

Finally, our pals arrive at Nadia's real homeland--Tartessos. As they tour through its long forgotten ruins, our heroine finally reveals her darkest secrets... including who she is. How will all this affect her relationships with everyone, especially Jean?

All the pieces fall into place for the final stage of Jean and Nadia's journey around the world, Nemo and Gargoyle's long-standing feud, and the secret behind Nadia's Blue Water pendant.

I won't tell you how it ends....