Swordspoint - Ellen Kushner

On the treacherous streets of Riverside, a man lives and dies by the sword. Even the nobles on the Hill turn to duels to settle their disputes. Within this elite, dangerous world, Richard St Vier is the undisputed master, as skilled as he is ruthless- until a death by the sword is met with outrage instead a of awe, and the city discovers that the line between hero and villain can be altered in the blink of an eye . . .