NOTE: If you betrayed Meeran then he could be waiting for you just south of Gamlen's House. Be ready for a fight if this is the case.
Leave Gamlen's House and enter Lowtown at night. Meet Anso the Contact in the Lowtown Bazaar and agree to help out. Enter the Abandoned House in the Elven Alienage, beware the trap - standard to your right as you enter. Open the eastern door to find a crate then go through the southern one. Defeat the Street Thugs and check the chest to find that it's empty. As you leave the house you are surprised by a group of Tevinter Hunters.
NOTE: While in Hightown you may run into Athenril if you betrayed her. She is near the Blooming Rose.
After the battle you will meet Fenris. Agree to aid him and head to Hightown at night. If you haven't search Hightown at night before then you can find a crate in the Red Lantern District. You can find Fenris in the Noble Estates just past the Chantry. After the scene Fenris is locked into your party and you must choose the other members. Once inside Danarius's Manor be sure to set up Fenris' abilities. Move to the door and disarm the trap - simple then fight off the Shades that attack.
As you move north into a larger room beware the numerous trap - standard that line the floor. Force the Shades to follow you into the previous room for a safer fight. The Rage Demon should be a top priority during this fight, but nothing that you can't handle. Back in the large room head up the steps and into the room on the left. Open the chest - standard then enter the room on the right to find a chest. Head back down the steps and go north until your reach a room with a chest. Loot it after defeating the Shades then go east.
Check the northern room first to find two chests , one holding a String of Pearls . Enter the eastern room and defeat another group of Shades accompanied by a Rage Demon. Loot the Rage Demon for the Magister's Key and search the chest . Return to the large room where you went up the steps, this time open the middle door. Doing so spawns an Arcane Horror and more Shades, be sure to prioritize the Arcane Horror first. After the battle a scene occurs and you are left to raid the three chests for a Slaver Lord's Cowl and a Torn Slaver Invoice . Return to Hightown where you have the option of recruiting Fenris based on your dialogue choices.
Head back into what is now Fenris' Mansion. Speak with Fenris to inquire as to the situation. Various dialogue options will allow you to gain a boost in Friendship or Rivalry as well as give you insight to his past. Read the book on the Adventures of the Black Fox then head up the steps in the next room to find a book on The Imperial Chantry . In the middle room you can find notes on the History of Kirkwall: Chapter 3.