Cyrus and the noble Constants have opened the Soterion vault containing the Long Dead's secrets of science, art and possibly even the cure to the mutation. Meanwhile, the barbaric Zeds are massing against them, determined to take the Soterion for themselves and destroy everything the Constants have built.

In a post-apocalyptic world where no-one lives beyond their teenage years, the mysterious Roxanne arrives in Cyrus's village, fleeing the barbaric Zeds. She claims to be on a mission that can save them all, but can she be trusted? Cyrus joins her in her quest for the legendary Soterion, but the Zeds are determined to get there first.