Thorn wants you to obtain a Sanctum Trial Stone and to start a ring event. The Sanctum Trial Stone drops from any Droag mob, and will drop when gray. (The discussion page mentions that this was changed in GU56 and a Trial Stone is no longer necessary, confirming that this is indeed accurate. Simply right click on the dragon statue mentioned below and choose the option "reach into the mouth".)
In the Hall of Rites, lower level of the Sanctum, there is a small dragon head statue at the base of a column inside the pit at ( 9, 54, -17 ) /waypoint 9, 54, -17. Right click and choose the 'insert the stone' to begin the ring event. Barriers will prevent you from leaving the pit while you work through the event, which consists of a first wave of 8 65^^^, second wave of 4 66^^^, third wave of 2 66^^^, then a 67^^^ named.
Note: There is a reuse timer on the statue. If the statue is not available for use, the insert option will not be available. The reuse time on the statue is estimated at < 1 hour.
Return to Thorn and she now wants you to kill the following:
After killing those the quest will auto-update, telling you to kill:
Kill 4 scaleborn banishers which are actively fighting Wraiths for auto-updates, found in the Reservoir of the Wraith room ( 72, 39, -158 ) /waypoint 72, 39, -158
Seek out the Severed Shade (in the same room as the Wraiths, on north side of Fountain) Touch the skull on the upper platfrom of the fountain.
Head back to Recovery Room and Soulclencher Volz will trigger in hallway ( 2, 37, -158 ) /waypoint 2, 37, -158 between Soulrend and Reservoir of the Wraith. Kill him for update.
Go to the forge ( -116, 65, -34 ) /waypoint -116, 65, -34, right-click it, and select "Break Open Metal Case" to complete the quest.