Investigate the Scourge of Darnassus

Objectives
Collect three Dim Necrotic Stones from the Scourge outside Darnassus and investigate the glowing runic circles nearby their encampment.
 * Investigate a circle
 * Dim Necrotic Stone: (3)

Description
The Lich King has sent his undead upon our very doorstep; we cannot remain idle! Surely you will step up to defend Darnassus from these accursed invaders?

There are strange runic circles outside, glowing with the same energy that surrounds the undead and the Necropolis above. They have significance, I'm certain, and I want you to find out what. Thin the numbers of those aberrations while you're at it; bring me proof of their death along with your results, and I will reward you. Go!

Rewards
You will receive:

Progress
Have you investigated the invasion yet? There's no time for dawdling!

Completion
Hmm. From what you've told me, the voices within the circles... they must be used for communication of some kind. I shudder to think what unnatural minds are contacted through such magic. Regardless, you seem to have emerged whole and sane. The Argent Dawn appreciates your service.