Ravencry (Raven's Mark #2) by Ed McDonald

Dark immortals never rest. Neither do the Blackwings who stand against them. Haunted by the bodies he's left in his wake, Blackwing captain Ryhalt Galharrow hunts spies, traitors and sorcerers along a blighted frontier of bad magic and vicious, mutated creatures. The remnant of apocalyptic war, the toxic wasteland he patrols has earned its name: the Misery. Beyond its twisted realities, the ancient Deep Kings plot their next move against the free states. When a garbled, frantic message from his godlike master sends Galharrow to an arcane vault, he finds its wards breached and an object of great power missing, propelling him into a race against time to return it. But in a city where new, insidious factions are rising and the corrupting influence of magic holds sway, can he trust even his closest allies? As Galharrow searches for the answers he needs, his journey will take him further and further into nightmare ... perhaps even to the Misery's twisted heart.