Forbidden Knowledge

Acquisition
Forbidden Knowledge is a quest you acquire from a letter in your Writing Desk in the Hawke Estate. You must have avoided killing Idunna during a quest in The Blooming Rose during the time before The Deep Roads. Idunna has sent you a letter: "Serah Hawke, Years past, I fell into wickedness and was swept up in the mad ambitions of the blood mage Tarohne. You spared my life at the Blooming Rose, and for many months, I wished you had killed me. But I found the Maker's Light in my deepest despair, and I now seek absolution.

Tarohne wrote many tomes containing dark secrets she learned from the Fade. She protected them with demons forged into their very bindings. You must find and destroy these tomes, lest others follow her dark path. I wish I could help you, but the templars never let me leave my cell. I can only send my prayers.

-Idunna."

Walkthrough
After entering an area with a tome, the map will show an arrow towards it. Be prepared to fight several packs of demons in each cave.


 * A cave at the west end of Sundermount, next to the western exit.
 * A cave at the east end of The Bone Pit (outside the mine).
 * A cave in the northern middle parts of The Wounded Coast.
 * In The Chantry, on a table up the southern stairs.
 * In the Viscount's Keep, eastern part on a table near the throne.

You Journal will update, and you will get information on The Fell Grimoire. It can be found in The Forgotten Lair, which is a cave in Darktown next to the entrance. Inside the cave there are several traps. Some of them are capable of killing most members of your party rather quickly so watch out for them, there's spaces where you can walk without triggering them. After destroying the Grimoire you will meet one of the most dangerous bosses in the game, Xebenkeck. The boss itself is not very hard but she will summon hordes of Rage Demon's and Abomination, as well as a Revenant in the second wave.

Result
The Fell Grimoire and Tarohne's tomes were destroyed.

Rewards
Voracity can be found inside the body of Xebenkeck and you are rewarded with the achievement "Exorcist" after killing her.