The Rifter, Book 4 of 10: Witches' Blood

When John opens a letter addressed to his missing roommate, Kyle, he expects to find a house key, but instead he is swept into a strange realm of magic, mysticism, revolutionaries and assassins. Though he struggles to escape, John is drawn steadily closer to a fate he share with Kyle—to wake the destroyer god, the Rifter, and shatter a world.