As a note, both the thief and the mage have some kind of interaction with the book once you open it, if you give it to them. Be warned, they won't give it up once they have it. You too, can read the book, which is a series of increasingly difficult wisdom saving throws.
Grants the thief or your MC the Speak with Dead spell 1/day on the first save (which is easy for a wizard MC). Mage (Gale) has no apparent benefit. Second and third saving throw do not seem to grant anything, although the description implies you might have gotten something if you were more powerful or invested in necromancy.
