Raised deep underground in the city of Solypse, Caelin dreams of life in the world above. Her dreams are crushed when she is coerced into service, plunging her into a world of spies, smugglers, assassins, and corrupt politicians. As Solypse negotiates a treaty with the city of Phira, a beloved war hero stumbles into secrets that could drive the political order of the depths into chaos. In the aftermath, they will have no choice but to try to save a mysterious nation from its own dark necessity, and in doing so, save themselves.