Candlewicke 13: Under The Crescent Moon:

Valor McRaven and Doomsy Gloomsy return to Mystic City where they are being hunted. While trying to become apprentices of magic at Mystic Steeples, they battle ghosts in a haunted mansion, investigate murders and disappearances, and travel back in time through a book that seems to be steering them closer to the truth of The Great Deception.