New humanity's greatest trump card—the intelligent mobile fortress Arcadia—has revived. The Empire is reduced to acting as Arcadia's puppet, Finn is ordered to assassinate Leon, and the last dregs of old humanity face total annihilation. Even Luxion can't hope to overcome the looming threat. Leon finds himself at a crossroads: does he take a select few with him and leave this doomed planet for outer space, or does he battle an impossible enemy where the only outcome is certain death?