When you get to the castle, you'll start in the dungeon. You will only have until morning to escape your cell and bag as much loot as you can find, but if the guards catch you, they'll throw you back in your cell. There's a list of items and the prices you can fence them for. There are rumors the castle is home to rare treasures that are NOT listed, so if you come across anything interesting... bag it. You might be able to get a special price. Only the best of the best get their names on the Blacklist, so don't waste a single second.