Ophala from the Moonstone Mask will request you to steal several artifacts from different men around the Blacklake and Docks districts. (If you're a rogue or have made a successful Persuasion check). If you accept you will have to acquire a statuette from Lord Androd Golden, a portrait from Lord Thoms Rumbottom, and an urn from a man named Hodge. Each one of them has a past with Ophala one way or the other. Their estates are large and ridden with guards so they make real good practice dummies for when you need to level up.
The first item is a Gilded Urn, you'll find this in the Blacklake District in one of the rooms inside the Hodge's Estate
The second item is also found in the Blacklake District - go on to the Rumbuttom Estate and look for Thoms Rumbuttom. After some good shakedown, he'll hand over the portrait of Sir Reginald Rumbuttom III.
The last item you'll need to acquire is a gaudy statuette. You'll find it in Lord Androd Golden's home at the Docks district. He will part with this item in exchange for his life so that's good. Note that all three estate will be ridden with guards.