City of bones

“Khat, a member of a humanoid race created by the Ancients to survive in the Waste, and Sagai, his human partner, are relic dealers working on the edge of society, trying to stay one step ahead of the Trade Inspectors and to support Sagai’s family. Khan soon discovers that the deadly trade politics of Charisat’s upper tiers aren’t the only danger. The relics the Warders want are the key to an Ancient magic of unknown power, and, as all the inhabitants of Charisat know, no one understands the Ancients’ magic.” - from MarthaWells.com.