It's been only year since Owen’s battle alongside the Resisters against the Harsh, who tried to destroy time itself. Cati, the bold Watcher who stands vigil over the Resisters, returns from the shadows of time to summon Owen and the ingenious Dr. Diamond, because inexplicable and frightening things are happening. The moon is moving too close to the earth, wreaking havoc with weather, tides, and other natural cycles. People fear that the world will end.

To discover what has gone wrong, Cati, Owen, and the doctor make an astonishing journey to Hadima, the City of Time, where time is bought and sold. There Owen begins to understand his great responsibility and power as the Navigator.