Last of His Line

Acquisition
This quest is obtainable in Act I if you've either imported a save from Dragon Age: Origins in which Prince Bhelen was awarded the throne of Orzammar, or you load one of the pre-made histories with the same condition (I believe the No Compromise one has this condition). Lord Renvil Harrowmont can be found in the Docks district of Kirkwall during the daytime.

Walkthrough
As you come upon Lord Renvil Harrowmont and his guards, they are attacked by several Carta Thugs and a Carta Assassin. Not a tough encounter. Once you've defeated the would-be assassins, Harrowmont asks you to help him clear the district of Carta members trying to assassinate him. From here you have the option of helping him out (which nets you a couple of gold in the mail), or turning on him when you meet the first set of Carta criminals.

If you decide to assist Harrowmont, start heading toward the west side of the docks (toward the Shady Merchant) and kill all Carta you see. Naturally, the first group gives you the option of killing Harrowmont, but since you've decided to play nice, kill them.

If you decide to assist the Carta in killing Harrowmont, head back to where you spoke with Harrowmont and he and his guards will engage you on sight. The Bodyguards have as much health as Harrowmont does (Elite rank, I believe), but it's still not a very tough fight.

Result
If you decided to help Harrowmont, he ends up escaping to Rivain. Whether or not he remains alive after that is not made clear.

Naturally, if you decided to help the Carta eliminate Harrowmont, then the entire Harrowmont clan dies with him. Not very nice.

Rewards
For assisting Harrowmont, you recieve one gold upon turning in the quest, and 2 more gold later on in a letter from Harrowmont. Total XP earned: 406 from killing Carta groups, 400 for completing the quest.

For assisting the Carta, you recieve 3 gold and 400xp (plus the little bit of XP you get for killing Harrowmont and his Guards). Harrowmont or his guards don't drop any loot, nor are you awarded any XP for killing them.