Waking nightmares - Christopher Golden

When chaos erupts in the small coastal town of Hawthorne, Massachusetts, former vampire-turned-mage Peter Octavian and earthwitch Keomany Shaw arrive to investigate. Years ago, Octavian helped expose the secret existence of vampires to the world, dismantling the Vatican's sorcery corps in order to save his fellow shadows from destruction. But without the Vatican sorcerers, the magical barriers they spent centuries constructing to keep the forces of darkness out of our world are beginning to fail, and things are slipping through.
Now an ancient god of chaos is awakening in Hawthorne, its influence spreading...and it's Octavian's fault. If he can't stop it, the blood of all human kind will be on his hands.