Investigate the Scourge of the Undercity

The Lich King has sent his undead upon our very doorstep; we cannot remain idle! Surely you will step up to defend the Undercity 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!