This quest is not available in game.
Travel to Dire Maul and locate the Imp, Pusillin. Convince Pusillin to give you Azj'Tordin's Book of Incantations through any means necessary.
Return to Azj'Tordin at the Lariss Pavilion in Feralas should you recover the Book of Incantations.
I had let my guard down for only one moment, stranger. In my haste to escape the grip of the fallen Prince, I was robbed. A most foul demon, the imp Pusillin, pilfered my book of incantations and the key to the once great halls of Eldre'Thalas.
I no longer hold interest in the key, as I have exchanged my immortality for freedom, but I desperately need my book of incantations.
Find the imp, Pusillin, and recover my book.
Search the Warpwood Quarter of Dire Maul for Pusillin.