It is the duty of the Vanguard to protect the world from unseen demonic forces.

But what if the organization falls to corruption? Their reformation is up to Cato, a disgraced former member who discovers many of the elite using their powerful positions and martial skills for ill-gotten gains rather than fulfilling their true purpose: aiding mankind in a secret war against their eternal foe.

Aldous is a Vanguard who fell from grace after being stricken with vampirism by a mysterious figure known as the White Lady. His increasingly vile appetites are tolerated because his knowledge as an alchemist is vital in the Vanguard's battle against the demons. When those desires lead to the abduction of the woman Cato loves, Cato wages a one-man war against Aldous and his werewolf henchmen.