The bansheeNightlash has established a base in The Dead Fields. When small expeditions have been sent in the past, some of the Rot Hide Gnolls have been slain, certainly. But each assault has been repulsed by Nightlash's magic, and the gnolls have been reinforced every time.
One of the things that High Executor Hadrec wants you to do is to go to the Dead Fields and dispatch Nightlash, returning with what dust remains of her corporeal shell.
You journey there, and discover a boat, heaped with corpses! It is clearly
evident that wherever these corpses came from, they are headed for
Fenris Isle.
A bit of glitter in the boat attracts your attention. On the hand of the
recently deceased corpse of a woman, you find a gold ring, with the
inscription "For Deliah".
When you bring the ring to Hadrec, he tells you that the only nearby source
for such a body would be the mass graves of Tirsifal. The Rot Hide
gnolls must be taking these bodies to Fenris Isle.
It is evident that something on Fenris Isle needs to be taken out. But just
what that is, and who is behind it, is still a mystery. More needs to be
discovered before an assault is made. Hadrec directs you to gather ichor
from the Rot Hides on Fenris Isle and bring it to Apothecary Renferrel.
It takes a bit (you manage to destroy many of the rot hides too thoroughly to
collect ichor from them), but you collect the amount Renferrel needs and
bring it to him.
Apothecary Renferrel reduces and analyzes the ichor as best he can, and does
discover some of its properties. It is not entirely alchemical, though, and
he asks you to take a sample to Bethor Iceshard in Undercity.
With his knowledge of magic, Bethor is able to divine more about the spells
involved in the Ichor... and who created them.
It turns out that the ichor was created by Thule Ravenclaw, one of Bethor's
colleagues who sided with the Scourge when the Lich King rose to
power. On the plus side, Bethor knows a lot about the magic that Thule uses,
and gives you a scroll that Apothecary Renferrel can use to craft a potion that
should counter Thule's more powerful spells.
You return, then, to the Sepulcher, where Renferrel concocts the potion.
Renferrel refers you back to High Executor Hadrec, who has access to the
Sepulcher's arsenal. Hadrec concurs with Renferrel that Thule must be dealt
with, and offers you some items to improve your armor and weaponry.
Armed and ready, you gather friends about you and set off. You have to
battle quite a number of Rot Hide gnolls as you work your way through the
castle, but finally you come face-to-face with Thule Ravenclaw.
Victorious in battle, you retrieve his head as proof that you have slain
him.
Returning to High Executor Hadrec, you are praised, and told that fallout
of your battle was felt as far away as the Sepulcher.