I am certain I am getting closer to identifying the secret faction behind the murders of Seeress Ealayna Ithis, Prophet of the Prime Healer, her Acolyte, and the Concordium Pupil Adepts. An important item that was to be protected due its usefulness in the void invasion has fallen into their evil hands. All the clues point to a secret group of elite, noble and eccentric members of different cities being involved, if not behind it all. I need to learn who they are and what they are attempting to gain.
Use the Stone of Obscuration in your inventory. Once you turn red (invisible) walk around in the crypt until you see NPCs. Stay as far away from them as needed to get the dialog popup and continuously click "continue to eavesdrop" until you are discovered.
The NPCs turn aggro; kill them all. Once a vessel is dead an amulet drops on the floor and the quest updates. (if you cannot find the amulet, zone out and back in - the amulet should be on the ground near where the vessel originally spawned)
Click the amulet on the floor. The quest updates again.
A cutscene called "An Out of Body Experience" plays in which you see an army of shadow brutes and shadowed men surrounding a hooded woman on a pillar of rock. Your own character can be seen floating to one side of the rock.