City of Bones

In a place where an ancient holocaust devastated civilization and caused most of the world's water to evaporate, a new civilization has arisen--where sand ships cross the deserts between city-states, where bones are used to work magic of all kinds. Charisat is the greatest of city-states, the Imperial seat where your status is determined by how high up the tiers of the city you live. Khat is a trader and sometime thief, one of a race genetically altered to survive in these new conditions. Elen is a scholar and a lady who is investigating the ancient ruins, looking for the secrets of their magic. Together they must solve a mystery involving a fanatical cult whose members are trying to unleash an evil that will topple Charisat--and from there, destroy the world again.