Forbidden Knowledge

Forbidden Knowledge is an Act 2 side quest in Dragon Age II.
 * IMPORTANT: Do not opt to read any of the books. Choosing to destroy all 5 books will complete this quest and you will be given a second quest that will give you the opportunity to defeat a boss, yielding kill exp. and loot, and the 2 attribute points you would have received for reading any of the books.

Acquisition
If not killed during Enemies Among Us, Idunna sends a letter at the beginning of Act 2. If she was killed the player receives the quest by finding any Evil Tome during Act 2.

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. This quest should be completed in the second act.
 * In The Chantry, on a table from the southern stairs, second floor.
 * In the Viscount's Keep, eastern part on a bench near the throne. After destroying the Tome and the Arcane Horror spawns the door is closed. This is a master lock so you need 40 cunning and the Caster's Skeleton Gloves to open and get some extra XP. To make sure you get the xp for lockpicking you must do it during the fight otherwise after the fight the door is open and you miss the xp for picking the lock.
 * A cave at the east end of The Bone Pit. Inside the location is called "Cave." The entrance is at a dead end on the right side of the map. It'll be an offshoot of the the map marker Bone Pit Mine. Corrupted Lyrium is also in the cave.
 * In Abandoned Thaig, the entrance (known as "Recently Opened Passage") is at the west end of Sundermount, in a corner left of the north-western exit, accessible only in Act Two. The tome is found in the main room of the thaig next to the Nexus Golem (for the battle in this room, see "strategy" section in Abandoned Thaig page).
 * A cave in the northern middle parts of The Wounded Coast. It should be named "Dank Cave" and is not marked on your map. Note that this cave is inaccessible later in the game. A Dragon guards the Tome and Treasure.  There is also Raw Lyrium at the beginning of the cave.

You can choose any of the following options when selecting a book (they are all mutually exclusive): Choosing any of these options will cause several demons and abominations to appear and attack.
 * (Destroy the book.)
 * (This applies for each book. Note: If you are in a relationship with Merrill there is no penalty for destroying the books.)
 * 750 XP
 * (Read the book.) > (Accept the book's deal.)
 * (This will only apply for the first book.)
 * Item received: Greater Tome of the Mortal Vessel
 * (Take the book.)
 * (This will only apply for the first book.)
 * Item received: Book of Forbidden Lore (trash item) worth US$8600.

Reading and accepting the books' deal will give you +2 attribute points, but this will only happen once, any books read after this will not provide attribute bonuses. Also, taking or reading any of the Evil Tomes makes the player unable to complete the quest, and the quest will remain in your journal. However, if you destroy all five Evil Tomes the quest will proceed and you will be led to the last book called The Fell Grimoire, which can trigger the boss Xebenkeck. If you read this book ONLY, you will be able to fight Xebenkeck, complete the quest and get 2 attribute points.

The Fell Grimoire can be found in The Forgotten Lair, which is an area in Darktown next to the entrance. Note that you may come across a locked door and will need a Rogue to unlock it in the Forgotten Lair. Inside the cave there are several Master level traps (40 cunning) that can be inconvenient when also being attacked. Ranged attacks can draw enemies into safe areas where they can be defeated and then the traps can be disarmed. NOTE : simple locked door(10 Cunning to open - 50 XP) and a complex trap & master trap (30 & 40 Cunning, respectively, to disarm - 150 XP & 200 XP) in the now-unlocked room. There have been some reports of NPC Rogues (Isabela and VArric) being unable to disarm the three Master-level traps even with 40+ Cunning. However, it has been CONFIRMED that a PC Rogue with 40+ Cunning can disarm with no difficulty.

After destroying or reading the Grimoire you will meet one of the games bosses, Xebenkeck, a powerful Desire Demon. The boss will summon hordes of Rage Demons and Abominations, as well as a Revenant in the second wave. See Xebenkeck (strategy) for tips on how to defeat it.

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

Rewards

 * Random loot
 * Voracity
 * Exorcist achievement or trophy
 * 1000 XP (for quest completion)
 * 730 XP (Xebenkeck and demons)

Bugs

 * The book in Viscount's Keep can not be immediately used upon arriving in Act 2, Hawke must leave the area and return to use it. Also true in v1.03, so it may have been the intended behavior.