How to Unlock the Hidden Eldritch Spell Page
To unlock the hidden spell page, ask the magic shop owner in the Village of Crowl about “Eldritch”. Note that NPC’s who join your party after that won’t have that page unlocked. The next person who can unlock that page will be a mage you meet after completing a series of puzzles. It’s Balderdash who is trapped in the Kublai Cathedral – ask him about “Eldritch” as well.