- Three air assassinations
- Two kills with the Phantom Blade during the final approach
Infiltration Opportunity - Sabotage the Chimneys
From your starting perch, you're going to want to enable your Eagle Vision, giving you the location of an Extremist directly below you, as well as two more who will patrol his area. Timing is key here. When the two patrolling guards turn and go the other way, perform an air assassination by pressing the attack button, then quickly move to cover the chimney to complete half of this objective.
With the chimney covered, climb back to the rooftops and wait for the patrol to return. When they do, they will inevitably discover the body, at which point you can score another air assassination, taking out the final Extremist with some of your expert sword work.
With that business out of the way, you should see a point of interest on your map, or a giant beam of light shooting up in the sky. This is the second chimney that you need to sabotage, so turn on your Eagle Vision and make your way over there. When that's done ,this objective will be complete.
Distraction Opportunity - Defend the Beggars
Another quick flash of your Eagle Vision should show another point of interest, and as you approach, it will update your objective and ask you to defend the beggars. You really want to do this in order to make your life easier in the later parts of the memory, but it's also a great place to score your final air assassination. Just make sure to clean up an stragglers, then get back to the rooftops.
Find the Hideout
The hideout that you're looking for is a sewer access point that sits behind a church to the northeast of your starting point. You could just parkour your way over there and go for an all out attack, but we'd advise holding off on following the advice that we've given to you above.
When you reach the church, notice the two Extremists who emerge from the sewer access point. If you're not completely sure you're in the right place, pop on your Eagle Vision to confirm. This is also a great place to pick up another air assassination if you still require one. Either way, kill the two Extremists and make your way into the sewers.
As soon as you enter the tunnels, you'll have three Extremists up ahead, and going straight at them is not advised. Instead, take cover behind the wall, then use the cover assassination mechanic to take out the one who patrols close to you. From here, you should have no trouble taking the final two out quietly. With them down, you can enter the sewers to complete your objective.
Find le Roi des Thunes
From this point forward, your path is going to be quite linear, and no matter how many Extremists you find, you should have no trouble sneaking past them or taking them out. Just be sure to constantly use your Eagle Vision so you always know what awaits you up ahead. Lastly, don't be afraid to observe your targets for a moment to study their movements.
You're going to need to make your way through three sets of guards before you complete this objective, and yes, you can sneak past all of them. Did we do that? No, we killed every last Extremist that was in our path. This is made far easier by purchasing the Double Assassination skill, but it's very doable even without it.
Assassinate le Roi des Thunes
Although it sounds like you're about to be in trouble, you're really not. You can continue to make your way through the sewers without worrying about anyone attacking you from behind. Just keep on keeping on until your map shows that you can go straight and into several Extremists, or that you can go left and completely bypass them. In this case, we're going to suggest that you simply bypass them. There really isn't a great way to kill them. Also note these are the very first adversaries you'll come across after the cut scene.
The next area is one where you'll find three more Extremists, and they are below you as you sit perched atop a beam. Study their movements for a few moments, then decide to either use an air assassination, or the Phantom blade to eliminate them silently. When they're down, make your way further on through the sewers.
A short distance ahead, you'll come to a gate that you can slide under, and La Touche can be seen standing on the other side. Slide under the gate, then wait for your foe to run away. This is also the point where you will unlock the ability to complete the challenge to get two Phantom Blade kills.
Make your way up a nearby ladder and then sit perched at the top. From here, you can use your Eagle Vision, but absolutely do not try and assassinate your target. That one, our assassin friend, is a decoy. Instead, make your way to the right, sliding under a gap in the wall.
Once you're on the other side of the wall, you'll come to a door, and using your Eagle Vision will give you a clear view of le Roi des Thunes. Again, forget this for now, passing by the door and up a nearby ladder. Once there, you'll see an Extremist. Kill this fool using your Phantom Blade, then hop your way around the room until you reach a locked door, picking it to gain access to your target. Once you're behind him, kill le Roi des Thunes with your Hidden Blade to complete the objective.
Escape the Area
Before you start to make your escape, equip your Phantom Blade and kill one of the Extremists below. Well, unless of course the challenge is already complete, in which case you should just make your escape.
Due to the fact you covered the two chimneys, visibility in the sewer is extremely low, but your Eagle Vision should give you a massive upper hand. Just follow the on-screen objective markers, killing your foes along the way. When you finally make your escape, you'll trigger the memory ending cut scene.