The last Secondary Quest to spawn from this Main Quest can be started in Hightown outside the Chantry. Speak with Magistrate Vanard to receive news of an escapee. Leave Hightown and go to the Abandoned Ruins where you will speak with Elren and Nabil about what's going on. You can choose whatever options you want at this point since you will be given an ultimatum later regarding the fate of the fugitive. Search the rubble on the ledge and enter the Ruined Passage.
As you move down the hall you will spot Giant Spiders off to the side. Go east and defeat the Raiders then open the chest - standard to find the Mont de Glace Stand . Backtrack and go north where you fought the Giant Spiders to be ambushed by more along with some Venomous Spiders. Loot them to receive the Spider's Silk Gland Plot Item then search the chest in the corner. Continue north until you reach a pile of bones then go east to a dead end where you will spot a chest guarded by a trap - master directly in front of it. Disarm the trap if you can and fend off the Giant Spiders that spawn behind you. Loot the chest for a Pewter Pendant of Wolves Howling at the Moon . Return to the junction and open the southern door into a large room.
A slew of enemies emerge in this room to include an Arcane Horror. Target the ranged first and keep your own ranged safe from harm. If you need to back out into the smaller hallway and funnel the enemies so that they are easier to control. There is a chest and a pile of bones in the room in addition to the plethora of dead creatures you can loot. Go south to find Lia, alive and well. As you move east there are two trap - standard in the way, disarm them or else they spring enemies on both sides.
As you follow the path you will run into Kelder. If you choose to kill him then you can leave immediately, otherwise a chase begins. Backtrack to the large room to find a new powerful enemy waiting, the Revenant. Defeat the foes then exit at the north then return to the Magistrate.