Return Gunther's Spellbook to him, on the island of Gunther's Retreat.
Long ago Gunther and I, along with the now Scourge Necromancer Thule Ravenclaw, were friends and students within the Kirin Tor - a society of mages in Dalaran.
Gunther and I both fell to the Plague, but I thought he either remained dead, or was raised into the ranks of the Lich King. It is good to know he is free.
We must have him. I have placed a spell on his book that, when he sees it, will show him that I too am free of the Lich King. After knowing this, it is my hope that he will join us.