Stones Unturned — Christopher Golden; Thomas E. Sniegoski

Behind the facade of a stately Boston brownstone, humanity's. lest defenses are being marshaled. Called to action by the enigmatic, brilliant man known only as Mr. Doyle, they hail from all planes of existence and are born from an array of supernatural and otherworldly backgrounds and bloodlines...

THE MENAGERIE
A powerful, demonic force has escaped from the infernal realm--putting the human world in dire peril. It seeks an ally in Danny Ferrick, the youngest member of the Menagerie--a changeling who is already tormented by his dark, primal urges, the legacy of his demon father. Tempted into sampling the horrific but thrilling existence of a full-fledged demon, Danny is on the edge of renouncing all that makes him human. Now time is running out for the other members of Doyle's team as they struggle to save their friend from falling into darkness--and taking all of humanity with him...