Tome of Dark Power (Plane of Knowledge)
In order to complete this quest you'll need to collect 8 pages of Dark Power from Plane of Nightmare, Plane of Innovation or Plane of Justice and combine them inside of a book you find in the Library of Plane of Knowledge. To start the quest find and speak with Councilman Srethix who is shown in the screen shot above.
Hail Councilman Srethix
/say What rare books
After you say this to him you'll want to go collect the Tome of Dark Power from the PoK library. It's on the first floor of the basement, I have provided two screen shots below to aid you in finding this book. It's on the bottom shelf near the slanted book but wedged up into the top of the bookshelf. I had to sit down in order to see it.
Once you have this book in hand you'll want to take it to the Plane of Tranquility and hand it to Elder Tal Almad. He's just to the left after you zone in standing around the large table inside the building. Hand him the book and he'll open it for you, returning to you the Unfinished Tome of Dark Power.
Now is the hard part! You'll need to collect 8 different pages of Dark Power from Plane of Innovation, Plane of Nightmare and Plane of Justice. Once you obtain all 8 of these place them inside of the Unfinished tome of Dark Power (as shown below) and hit combine. This will complete the book which you'll then want to turn in to Councilman Srethix back in the Plane of Knowledge.
For those who want a redacted version of the list:
Page 2 of Dark Power
Page 3 of Dark Power
Page 5 of Dark Power
Page 7 of Dark Power
Page 11 of Dark Power
Page 13 of Dark Power
Page 17 of Dark Power
Page 19 of Dark Power
These items have a random chance of dropping off different enemies in Plane of Nightmare, Disease and Justice. You'll need to do endless hunting in all three in order to accumulate all of these pages. When I completed this quest just to write this guide it took me about 6 full clears of Plane of Innovation and one or two of Plane of Nightmare. That totals to about 5000 + enemies.
Due to the difficulty involved in acquiring all of these pages I don't recommend you even bother starting this quest until you've looted all 8. You can loot them before hand, prior to starting the quest so it's no big deal. Once you have all 8 then do the rest of the quest.
And you're probably wondering what the reward is for this quest... Well, it's a cloak that's shown below!