Echo City by Tim Lebbon

Surrounded by a vast, poisonous desert, Echo City is built upon the graveyard of its own past. Most inhabitants believe that their city and its subterranean Echoes are the whole of the world, but there are a few dissenters. Peer Nadawa is a political exile, forced to live with criminals in a ruinous slum. Gorham, once her lover, leads a ragtag band of rebels against the ruling theacy. Nophel, a servant of that theacy, dreams of revenge from his perch atop the city's tallest spire. And beneath the city, a woman called Nadielle conducts macabre experiments in genetic manipulation using a science indistinguishable from sorcery. They believe there is something more beyond the endless desert . . . but what?

It is only when a stranger arrives from out of the wastes that things begin to change. Frail and amnesiac, he holds the key to a new beginning for Echo City--or perhaps to its end, for he is not the only new arrival. From the depths beneath Echo City, something ancient and deadly is rising. Now Peer, Gorham, Nophel, and Nadielle msut test the limits of love and loyalty, courage and compassion, as they struggle to save a city collapsing under the weight of its own history.

From the Paperback edition.