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....

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.

After relocating Jean, Nadia, Marie, and King to his personal quarters (which he will later jettison from the doomed Nautilus), Nemo finds Electra holding a gun on him. In an extended flashback sequence, Electra reveals her tormented past, her complicated feelings for the captain... and a horrifying connection between Nadia and Nemo.

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?