Doomcaller's Attire

Doomcaller's Attire is the Brood of Nozdormu set for warlocks.

Source
Doomcaller's Attire can be acquired through quests given by Andorgos, Kandrostrasz and Vethsera, who can all be found inside the Temple of Ahn'Qiraj.

The quests require a given reputation with the Brood of Nozdormu, and  (which drop from trash mobs in the Temple of Ahn'Qiraj) and a token from a boss in the Temple of Ahn'Qiraj.