Summary: Part One in the "Penumbra" Series.
They call it the War of Blood, a cataclysm which will decide the fate of all sentient life and of wizardry. The Wizarding World is diseased, but Voldemort is just the canker. The worst elements of wizardry have now gathered, not only Death Eaters and Dementors, but all elements of darkness, because underneath it all, invisible to most but nonetheless present, there is an ancient war raging.
As he departs on the Horcrux Hunt, Harry Potter finds an unexpected ally. After he disappears, the unrest and corruption in the Ministry starts making things difficult for the Order and easier for the Death Eaters, Voldemort has found a new and deadly ally, and in the meantime, an elite group of goblins begin planning their own fight against Voldemort.
Summary: As Harry begins his quest for the remaining horcruxes, his world is turned completely upsidedown by the return of Severus Snape, and Harry learns more than he ever thought possible about Snape, his parents, and the burning question of Dumbledore's death.