This quest is not available in game.
Use the Brazier of Beckoning to summon forth the spirit of Mor Grayhoof and slay him. Return to Bodley inside Blackrock Mountain with the recombined Lord Valthalak's Amulet and the Brazier of Beckoning.
My friend, Mor Grayhoof, was the first to fall victim to possession of a piece of Lord Valthalak's amulet, and the corrupting spirit fragment that it contains. After stealing Valthalak's spellbook and amulet, we fled for our lives from the upper portion of Blackrock Spire. Along the way, Mor fell into the lower portion of the spire.
Later, we discovered that he survived the fall, only to be captured and tortured by War Master Voone. A few spectral assassins snuck in and slew him right in front of Voone.