You decide to see what the book on the bookshelf, and see what was special about it. From the cleanliness of the cover, it looked nicer than the other books that have burned down when the castle was destroyed. You pulled the book out of the bookshelf, and noticed the other books began to turn into dust after pulling that one out.
You never thought a book like the one you pulled out would survive throughout so many years, but when you opened it up, you discovered there was more to the book, than just surviving the destruction of a fire. You open the book, and discover that it was used to either transform a human into a monster, or summon an artifact that could transform someone into a different creature. You didn't know anything about using a spellbook to transform anyone, or summon something, but you wanted to give it a try.