This quest is not available in game.
Use the Brazier of Beckoning to summon forth the spirit of Isalien and slay her. Return to Bodley inside Blackrock Mountain with the recombined Lord Valthalak's Amulet and the Brazier of Beckoning.
It became known to us in later days, as we were doing what we could ourselves to survive, that Isalien, a night elf priestess of our company, had gone to the night elvic ancestral city, now known as Dire Maul. From what we gathered, she went there both for personal reasons and also to unlock the secrets of the piece of the amulet that she had in her possession.
She didn't quite make it, though. Word got back to us that she was ambushed at the Shrine of Eldretharr by Alzzin the Wildshaper and his forces.