A Reliquary of Rust. The Nephilym Chronicles, #6

A falling angel is a heavy burden on a mortal soul. A living plague is a death sentence for a kingdom with a rotting past. Sire Andre Carthys was prepared to die at his King's feet for the crime of sorcery. Instead, King Almyr gave him the title of the King's Falcon and sent him and his soul-bound angel to defend the kingdom alone. Now, six chapters into a saga written in divine blood and mortal sins, time is running out. When a voice from the grave reaches out to haunt his dreams, Carthys is drug back to the Tomb of Loriene-where the air is thick with rust and the walls lined with nameless bones.
The Nephilym of Pestilence has been freed of its chains, threatening the kingdom with a festering blight if allowed to grow unchecked. With the angel Valiant fading, the king's falcon can no longer rely on blind miracle to keep him alive. To stop the forces of the fallen from growing, Carthys must decide if he is a harbinger of the Light-or just a man unwilling to lay down and die.