Midnight Magic (Scholastic Gold) (Midnight Magic #1)

Night after night, a ghost appears in the royal castle of Pergamontio, terrifying the princess. Mangus the Magician doesn't believe in ghosts, but still the King charges him with finding this one and freeing his daughter from its torment. If he can't, Mangus will pay with his life. The magician's only hope is his faithful, street-smart servant boy, Fabrizio, who must solve the mystery of the ghost using logic and reason -- and a bit of magic of his own.