«Ghost Relics» by Jonathan Moeller

Caina Amalas is the Ghost circlemaster of Istarinmul, the leader of the Emperor's spies in the city. She is a master of stealth and disguise, and faces foes of terrible power.
So when an ancient relic of necromantic sorcery is discovered, Caina must destroy it before it kills uncounted thousands of people.
Starting with her..