I suppose an explanation is in order. You've met one of the archmage's apprentices, Ravandwyr, but there was also another named Naberius.
He was an ardent student, but was drawn to necromancy. When Kael'thas appeared with his forces, Naberius seized the opportunity to betray the archmage, handing over the secrets to the tower's defense.
Now, it seems, he has become a lich. If we are to stop him, we must capture his phylactery. Knowing him, he would've buried it somewhere out of sight in his domain.
Rewards
You will recieve: 1 3 20
Progress & Completion
You must recover Naberius's phylactery before we can attack him. Otherwise, he will be invulnerable.
Excellent work, Yohaan. Possession of the phylactery will be the key to our victory. When you enter battle with Naberius, I will smash it, exposing him to your attacks.
Malevolent Remnants - (Step 1) Custodian Dieworth at Kirin'Var Village wants you to defeat 20 Severed Spirits in Kirin'Var's Town Square.
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The Annals of Kirin'Var - (Step 2) Retrieve the Annals of Kirin'Var from the town hall of Kirin'Var Village and return it to Custodian Dieworth.
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Searching for Evidence - (Step 3) Search Kirin'Var Village's Chapel Yard for clues about who is behind the manipulation of the spirits.
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A Lingering Suspicion - (Step 4) Collect 10 Loathsome Remnants from the twisted spirits in Kirin'Var Village's Chapel Yard and bring them to Custodian Dieworth.
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Capturing the Phylactery - (Step 5) Recover Naberius's Phylactery from Kirin'Var Village's Chapel Yard district and bring it to Custodian Dieworth.
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Destroy Naberius! - (Step 6) Custodian Dieworth in Kirin'Var Village wants you to confront and defeat Naberius in the village's Chapel Yard.