While her starfaring people are being hunted by an implacable enemy, a young caver discovers a traitor in their ranks and must undertake a transformative journey across the galaxy to save everything she has ever known. Persecuted for their worship of the Endless—an ancient, galactic-spanning race of god-like power, who disappeared long ago—the Pilgrims escaped the world of Raia almost a century ago, fleeing the despotic rule of the United Empire in a dozen space-faring fleets. The Pilgrims of the Horizon of Light fleet have spent two long years being hunted by an especially determined Empire foe. Now though, it appears they've finally caught a break, laying low on a non-descript comet that's hurtling into deep space. Young Pilgrim Sewa Eze wants to become a caver—and head into the depths on deserted moons, asteroids, and worlds to secure whatever the fleet needs: precious resources, Endless relics, even Dust. However, a strange device is discovered deep in the ice of the comet they shelter on—suggesting dark forces are afoot—and Sewa is instead selected for a leadership role at the Ceremony of Duties and must reassess her life, beginning with finding the traitor in their ranks who threatens her entire fleet's existence. The course of Sewa's life changes forever as she is forced to confront treachery, discover the secrets of the ancient past and travel to the very heart of the tyrannical United Empire.