Journeying through the Ash Sea , the twins confront their shared trauma: flashbacks reveal their childhood in a fragile Martian habitat, their father’s obsession with "rebalancing" Earth’s biosphere (which led to a failed geoengineering project), and Vio’s choice to stay on Earth to "atone." The pair clashes over methods—Abby’s tech-first ideals vs. Vio’s "rewilding" ethic—until a near-death encounter with a pack of irradiated wolves forces them to trust each other.