- Sabotage three alarm bells
- Perform three cover kills
Infiltrate the Palace
From your starting position you can see the window where you'll be entering the palace, and it's just to the southwest, in the corner where the two buildings meet. In fact, you should see a wooden platform just below the window. The problem that you face, however, is that there are a lot of guards between you and your objective, meaning you'll need to take a bit of a detour.
Run to the south along the rooftops of the building you're currently on, then drop to the ground level and cross the street. From here, climb up the building on the south side of the street, then start making your way west (toward the window we mentioned). Be on the lookout for a single guard, avoiding or killing him before you climb up the taller building that connects the one to the south with the one to the west.
If you look at the rooftop of the building on the west side of the courtyard you should see two bad guys, both of which can be killed using separate Air Assassinations. Do so, then it's time for you to make a big decision. If you want to complete the challenge to disable the alarm bells, continue reading. If you are cool to skip it and move on, the following paragraph is of no use to you and you can jump to the part where we infiltrate the palace.
From your current position on this rooftop there is one alarm bell to east, just on the ground level between where you are now and your starting point. There are also two alarm bells to the west, over the rooftop and at the ground level of the building. If you're having a hard time spotting them, try using your Eagle Vision to make it easier. We opted to skip the alarm bells and just proceed with the mission, but if you want to complete the challenge you'll need to make use of your Double Air Assassination, taking out the guards that patrol the areas around the three bells. When you've completed the challenge, return to the rooftop where you performed the two Air Assassinations.
You should now be on the rooftop that you need to drop from in order to infiltrate the building. The wooden platform we mentioned earlier, it's on the south side of this roof, just below you and wedged into the corner. Climb up on the balcony, then perform an Air Assassination to eliminate the Extremist below. From here, use your Eagle Vision to make sure the coast is clear, then sneak inside.
Find the King's Office
As soon as you're in the building you're going to want to turn right and sneak toward the next room. You should see an overturned couch, and when the coast is clear you'll need to take cover behind it, popping out to neutralize the Extremist for a cover kill. That will be the first of three that you require.
Make sure that the patrolling Brute isn't headed your way, then sneak back to the area where you first entered the building. Eagle Vision should show one Extremist pounding on a door, plus one Brute that is roaming back and forth. The dude at the door is no trouble, so wait for the Brute to patrol into the room where you just killed the Extremist, then eliminate him with a cover kill. With your foe down you can either kill the final guy at the door or leave him. We chose to leave him just to ensure that there weren't extra bodies laying around for our adversaries find.
If you head north you'll see a set of stairs that go down, then back up. That's the way you're headed, so use your Eagle Vision to ensure the coast is clear, then sneak behind and take out the guard on the landing. Keep moving up, snatching your final cover kill on the enemies in the next room. With them down, get back to heading north.
Your Eagle Vision should now show you an Extremist confronting a soldier, but soon after the soldier will be out of the picture. Quickly sneak up and kill the extremist, then take out his Brute friend as well. From here you should be able to move through the giant door and trigger a cut scene.
Find the Iron Cabinet
This is on the south side of the room and will actually have an objective marker. Walk up to the cabinet and interact with it.
You've got several waves of bad guys that intend to do you and Napoleon harm. It's just standard melee combat, but you can also use Smoke Bombs to make things easier on yourself. Don't forget to heal up if you take damage, but when the last foe is down you'll trigger another cut scene.
There really isn't any difficulty here, just walk and talk with Napoleon until the memory is complete.