Ghost price (world of ghost exile short story)

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 thieves try to burn down the home of an impoverished widow, Caina sets out to help the old woman.  But the widow's dead son had a secret. A secret that might lead Caina to her death...