Arno needs to get out of the palace undetected. This can be a little tricky if you don't know where to go. The first open door is on the far side of the guard who is patrolling the area. Start using Stealth to slip over to the first table. Head along the table to the left and shift cover over to the next table. Get to the end of that one and look to the North. You will see a covered couch. Wait for the guard to turn his back and move over there. Slip around the other tables and through the doorway. The next hallway is empty so head to the far end of it, still sneaking.
Head into the next room. There is a guard looking at the fire place. Just keep sneaking and head over to the desk. Watch the guard a moment then sneak through the door ahead of you on the right. Go over to the table on the left and take cover behind it. Move to the table that is just ahead of you on the left.
Slip carefully along the wall-side of the table. You need to watch the guard in the room. He will be periodically turning around and looking toward the wall. Watch for him turning. If he does spot you, just be sure you are in cover and he will quickly lose sight of you. Head to the South and exit this room from the door while his back is to the wall.
This next room has 2 guards in it. They are not the most observant. Just head to the covered couch that is nearby. Slip over to the far end and then make your quiet dash for the open door to the right. Just head on outside after that you are in the clear.