This is a group (5) quest. The Cabal camp is located in the center of the Lake of Solace. Use Visage of the Deep near the camp (but out of agrro radius of the mobs) to mask yourself. After you do, there will be a stone lit up. Right click the stone to study its writing. After you do Tideweaver Gelaine will appear behind the big rock. Speak with her. After she speaks with you, you will be in combat with har, and the whole camp. Simply kill all the mobs. The Faceless Man's Soul Shard will be lootable in the center of the camp. Return to Faceless Man in the Office of the Unseen in Meridian to complete.