Years after the mysterious death of her father, sixteen-year-old Josie Owens wants nothing more than to carry on his legacy as an engineer aboard November's Dawn. This colossal walking ark has traveled the bottom of the oceans carrying the last remnants of humanity after an all-consuming flood. But Josie's dreams drown when she discovers the secret her father died for: the ark was never meant to stay submerged.

This knowledge makes Josie, and those she loves, an instant target to those who would sacrifice anything to keep the status quo from changing and to those who want nothing more than to upend the firm hierarchy. At the same time, a glitch in the navigation system sends November's Dawn directly toward a miles deep trench.

Faced with a multitude of challenges, Josie wonders if pursuing her father's last wishes is worth the cost. Corruption and injustice permeate the last vestiges of humanity, but what if the great unknown of the world above is worse than their fragile existence below? If she follows her father's vision, the ark could be destroyed on the surface. If she follows the rebels, revolution could tear the ark apart from within.

One way or another, Josie is the only one with the knowledge to make the final decision. If she makes the wrong one, not only will the ark fail, but the last spark of humanity will fade into darkness.