Bring Bethor's Scroll to Apothecary Renferrel at the Silverpine Sepulcher.
This Ichor was crafted by an old colleague of mine: Thule Ravenclaw. He was a young, promising mage before the great war, but when the Lich King rose to power, he betrayed his brethren and allied with the Scourge.
I did not realize he still lives, nor that he leads the Rot Hides in their forays against us!
I know many of his spells, and can help concoct a potion to counter them. Take this scroll back to Apothecary Renferrel. It has the incantations needed for the potion.