Justice is all Xylo craves. His enemy has escaped into the unknown, taking nearly 40 others aboard the skyboulder-among them, the grandchildren Xylo never knew he had. Determined to bring his enemy back to face the consequences of the destruction he's wrought, Xylo embarks on a mission that will lead him to the unexpected-for better or for worse.

Twelve-year-old Tass has never felt more alone. Her only friend is dead, and her sister-whether alive or lost forever, she doesn't know-has vanished aboard the skyboulder. Desperate to find her, Tass faces a perilous journey, torn between saving her sister and losing herself along the way. Can she survive the search without sacrificing her life... or her soul?

Talag has always been an outsider. When his grandfather chose him to board the skyboulder, one of the few selected to create a new world, Talag was left confused and out of place. Now, with his unlikely companion-an elderly, intellectually disabled man named Dynny-Talag must confront his family's dark secrets and his own role in their legacy. As dangers mount, can he and Dynny find a way to save themselves before it's too late?