Harry Potter and the Shadow Hunter

After the death of his godfather Harry is an angry young man. Locked in his room like a prisoner he reaches his wits end. Desperate for any hope he discovers a new power that can change his life forever. Death Eaters will never be safe again as Harry takes matters into his own hands. Assume canon through the end of OotP. From that point on...anything goes. No horcruxes. Grey Harry.