Oath of Iron and Bone. Oath of Iron and Bone, #4

In a walled city that stinks of desperation and death, the hunted warrior Corius is hiding from his past. But he cannot hide from his present. Bound by a debt to the ruthless assassins of the Four Swords, he lives and dies by a single code. His next contract is his most chilling yet: murder Lady Dangerosa in cold blood. The order comes from the one man she should be able to trust-her own wealthy father, who fears her "dabbling in sorcery." Could be a danger to his own growing power.
Watching him is Dombyr, a fellow killer whose quiet threats are a chilling reminder of the price of failure. To the Four Swords, betrayal is a debt paid only in death. Corius is a loose end, and he knows it; the Four Swords bury their secrets along with their assassins.