Earth is under attack by the alien Authority. Cassius Stevenson and his brother Jesse Fisher, descendants of the planet Haven's resistance forces, are the catalyst and key to marshalling Earth's remaining resources and warding off the invasion.
But the Authority has only begun to fight. Their terrible new weapon sends Earth's defenders-Skyship soldiers, the Surface government, and an army of Drifters-into turmoil.
Alliances shift, traitors are revealed, and soon Earth's last chance at salvation lies in the hands of one brother who must make the ultimate sacrifice.