This Dragon Age 2 sidequest, entitled 'First Sacrifice', is pretty aptly named. You'll be helping a man named Ghyslain search for his lost wife, whose fate has not been entirely pleasant. Check out these four videos for a full walkthrough.
From the Creator:
1. Find the Help Wanted sign in the market in Hightown (Day). Go up the stairs and speak to Ghyslain de Carrac about his missing wife, Ninette.
2. Travel to the Blooming Rose brothel and speak to Jethann.
3. Go to Darktown (Night) and find the Meeting Place. Fight through the street thugs and speak with Emeric.
4. Travel to Lowtown (Night), and find the Foundry. Fight the various demons inside and make sure to gather the ring from the dropped loot. Travel to the Gallows to speak with Emeric, and then return to Hightown (Day) and speak with Ghyslain de Carrac to complete the quest.