Koltira, aboard Orgrim's Hammer, wants you to collect 5 Dark Matters and summon a Dark Messenger at Aldur'thar.
Alright, friend, time to plant a bug.
Relax, it's not a bug exactly, but it'll serve our purposes.
In the northern portion of Aldur'thar, the cult's void summoners enslave demonic minions. Use this rod to siphon the dark matter from the corpses of these enslaved minions, and then use the cultists' summoning crystal to bring our little spy into being.
Until it is discovered, the messenger will serve as our eyes and ears, discreetly observing the actions of our enemy.