Terminal World - Alastair Reynolds

Spearpoint, the last human city, is an atmosphere-piercing spire of vast size. Clinging to its skin are the zones, a series of semi-autonomous city-states, each of which enjoys a different - and rigidly enforced - level of technology. Following an infiltration mission that went tragically wrong, Quillon has been living incognito, working as a pathologist in the district morgue.