The
Bestiary is a book found in the
Labyrinth, on a remote island near Ireland by Lara when she was a teenager. It contained a list of the names of all demons that existed. Lara needed the book to name the demon
Verdilet who had taken
Father Patrick hostage. Once you name a demon, you have control over it. The bestiary was left in Ireland at the very spot where Verdilet disapparated.