Medieval mysteries (Avi)

In Italy in 1491, Mangus the magician and his apprentice are summoned to the castle of Duke Claudio to determine if his daughter is indeed being haunted by a ghost.

Mangus the Magician and his thirteen-year-old servant, Fabrizio, are commanded to go to Venice, on pain of death, to find a book by Friar Luca Pacioli which reportedly contains a magical means of making money; but Venice is a strange and dangerous city, and someone else is also after the book--then Mangus is arrested, and taken to the prison, and Fabrizio and Bianca, an orphan he has met, must find a way to secure the book, save Magnus, and themselves....