The Secret of Secrets
The Secret of Secrets is a book of arcane magic written by Agnes of Glanville, the first human woman to become a sorceress. She was a member of the first Chapter of the Brotherhood of Sorcerers. It was also one of the tomes which was part of Ciri's curriculum in Ellander while she was studying with Yennefer at the Temple of Melitele. Ciri only flipped through this one and never finished it.
The title of this book is "Mystery of Mysteries" in the game.