City of Bones is the second book by Martha Wells that I’ve read, and the first standalone of hers that was published.
Charisat city is the Imperial Seat from which the Elector rules, and a wonder amongst the deadliness of the Waste. It’s a city of promise, a place where the tier you live on determines your station in life, and the amount and quality of water you consume. In this great city Khat, a Kris born in the Waste, and Sagai, a foreigner from a different city, have sparked a great partnership as antiquities dealers and even a greater friendship. They make a decent living for themselves and Sagai’s family on the sixth tier, but all of that changes when Warder Elen hires Khat to be her guide in the Waste, upending their lives forever.