Elder Casian:
In order to obtain the pieces of the spellbook, you must conquer the ant recruits, ant patrols, ant guards, the noble ant and the noble ant leader.
Check carefully any scraps of paper you come across. The pieces of "Kranvel's Spellbook" should be easy to identify.
The spellbook has four chapters: the Chapter of Fire, the Chapter of Water, the Chapter of Wind and the Chapter of Earth. The contents will only be discernible if you recover all four chapters.
This is a challenging task, but I think you are ready for it. May the divine blessing be with you...