Dragon Age 2 - Loose Ends is a short side quest from Meeran, the mercenary Leader. In this walkthrough you can choose to either support Meeran and kill the noble after the fight, or spare him, which leads to more choices when confronting Meeran afterwards.

1. Pick up the quest from a letter on your writing desk (make sure to accept the letter to actually get it).
2. Speak with Meeran in Lowtown at Night. Accept his proposal.
3. Head to the docks at Day
4. Follow the quest arrow and speak with Gustav.
5. In this lengthy fight, make sure to keep the archers and melee attackers away from your casters (mages).
6. Put your tank party member on the Guard Captain and take him out later.
7. After the dialogue you can choose to kill or spare the Lord.
8. Go to Lowtown at night and speak with Meeran to complete the quest.