Sam is searching for an Ozuma, or “sand whale,” when he spots a woman being chased by the Theseus Army. When an Ozuma appears and causes the military to turn back, Sam rescues the woman, who introduces herself as Maya. Sam takes Maya back to the ship he lives on to let her eat, but the Theseus Army catches up and corners the ship, demanding Maya. The captain decides to protect Maya, and the military opens fire. The ship escapes by diving into the desert sand, much to the surprise of the Theseus commander.

The Sand Pirates have escaped with Maya, and Theseus is in hot pursuit. The pirates dive under the sand, but are locked down by sand anchors. The pressure and temperature in the ship are rising, and time is running out.

Sam takes Maya to a hidden shelter constructed in the distant past, and filled with ancient technology. This shelter is the source of the ship’s technology, and the secret of Sam’s plans to hunt the sand whale.

As Gido escapes with Maya, Sam sets off in pursuit with Mimay in tow. But their bike is no match for the Theseus sand cruiser, and Gido escapes. To catch them, they’ll have to go back under the ground with the Bardanos.

The Bardanos finds itself in Ozma’s nest: a strange cave filled with fresh water and life. Bainas shoots Gido’s mask, and the face beneath it is that of Sam’s brother.

Ozma’s nature is revealed, and it’s time for Maya to make her choice: begin a new era with the life inside the zone, or allow humanity to remain in control of a dying planet.