The Divide is flooded, at great cost of human - and inhuman - life. Far from home, Sal, Shilly and Skender seek the source of the deluge in the legendary Hanging Mountains, traveling in a magical ship of bone. New threats await them in the fog forests of the Panic, and new tests of their friendship. Caught in a conflict that erupts between two long-forgotten civilizations, they struggle to discern ally from foe, and to find trust when it is needed most. In their wake comes the Homunculus, vessel and prison of the Castillo twins - sole, strange survivors of the catastrophe that changed the world forever, a thousand years ago. Their mission is paramount, their urgency contagious. Something much darker and deadlier than the Swarm is stirring in the heart of the mountains. And for Habryn Kail, already assumed dead by his masters, it might really be the finish of him, this time ...