This quest is not available in game.
Speak with Gan'rul Bloodeye in Orgrimmar.
You there. <name>, right?
I hope your schedule isn't busy, because Gan'rul wants to see you right away. You'll find him with the senior warlocks in the Cleft of Shadow.
Based on my past dealings with Gan'rul, your summons is either a very good thing or a very bad thing.