Thassarian at the Wailing Ziggurat wants you to go to the Temple City of En'kilah and retrieve High Priest Talet-Kha's Scroll from the Spire of Pain, High Priest Naferset's Scroll from the Spire of Decay and High Priest Andorath's Scroll at the Spire of Blood.
Go to the Spire of Blood, the Spire of Pain and the Spire of Decay and slay each of the priests.
Return once you've obtained the three scrolls.
Taking your time, are you? I don't know how much longer I can keep this lich restrained.
Excellent work, <name>. Now for one last bit of information.
The Spire of Blood has a 2nd floor around the side; that is where the priest will be.