Thief Side Mission: The Rule Of Thumb

This is another place that you have to look up to enter. Look for the open trap door, and shot an arrow up. Climb into the room, and open the window inside. There is a man walking around the wooden room with a lit torch. Let me repeat, there is a man with a huge flame, walking around a small room filled with flammable items and drapes. Kill this idiot before he sets the whole city on fire, and loot the place.

Inside a cabinet is a rare, highly valuable, vase. Smash it and push the button that was hidden behind it. Grab the Iris Brooch, and head back to the pyromaniac. He has the item that you're after on him. Just pick him up, and you'll collect it. Throw the body, and leave.