Sabotage the chimneys, defend the beggars and assassinate le Roi des Thunes.
Assassin's Creed: Unity guide - Sequence 4 Memory 2: Le Roi Est Mort - Find the Hideout
There are plenty of opportunities to complete the optional challenges throughout this mission. We'll alert you to the best ones, but feel free to experiment.
- Three air assassinations
- Two kills with the Phantom Blade during the final approach
Infiltration Opportunity - Sabotage the Chimneys
Your first task here is a slightly tricky bit of stealth, so without moving from your starting position, glance down and switch on Eagle Vision to spot a lone Extremist directly beneath you and another two patrolling nearby. Watch their routines, wait for the two guards to turn and walk in the opposite direction, and perform an air assassination on the lone Extremist. Don't hang about puffing up on your glory; quickly interact with the chimney and get back to the rooftops before the pair of Extremists comes back. When they come back and start freaking out, take one more out with another air assassination (we're aiming for three, remember?) and dispatch the other - quickly! - with your sword.
Look for the second chimney; with Eagle Vision on, scan the skyline for the beam of light. Wander over there and complete the objective.
Distraction Opportunity - Defend the Beggars
Before moving on, use Eagle Vision and scan the skyline again; there's another point of interest worth checking out, which will trigger this optional objective. It's definitely worth doing as it makes later objectives easier, and you can also take this opportunity to nab another air assassination, finishing the first optional challenge. Just take down all the baddies before returning to the rooftops.
Find the Hideout
The approach to the hideout (a sewer access point) is easiest if you play it smart. Head on over towards the church and put Eagle Vision on; you'll quickly spot two Extremists exiting the relevant sewer access point. Take them out and invite yourself in.
Inside the hideout entrance, take cover behind the wall; there are three Extremists directly ahead. One will come close enough for a cover assassination, which makes it much, much easier to take the other two down without alerting them. Easy as pie, right? Head on into the sewers.
Find le Roi des Thunes
The trek through the Extremists' hideout is pretty easy, actually. There's only one path forward, and as long as you use Eagle Vision judiciously, the guards tend to be easily avoided or assassinated if you just study their patrols for a few moments. They won't come after you later on, so kill or spare the guards as you like; there are three sets between you and your goal - a cutscene.
Assassinate le Roi des Thunes
After the cutscene you can enjoy a gentle stroll through the sewers without meeting any enemies for quite some time. When you finally run into a group of three guards, there's a path to the left that lets you bypass them completely. Do it; for some reason, these guys are slightly smarter than usual and fail to walk into ambush points. There are better targets ahead.
Press onwards to emerge onto a beam and spot three more Extremists below you. Watch their movements and you should see a couple of ways of taking them out quickly and quietly; Phantom Blades are great, and you can take down the last one with an air assassination if you're yet to complete the challenge.
We're just about to enter "the final approach", which is where you need to score two Phantom Blade kills, so keep that in mind; I'll point out both opportunities. Move forward until you see a gate, with La Touche on the other side. You need to slide under the gate, which sends La Touche running for his life.
Don't stress out; he's not your target. Climb the nearby ladder and sit at the top, activating Eagle Vision to get the lie of the land. There's a gap in the wall to your right you can slide under. Head towards the nearby door and switch eagle Vision on to spot le Roi des Thunes; we're not going for him yet, but it's nice to know where he is.
Look for another ladder and climb up to find an Extremist you can kill with the Phantom Blade - that's one. There's a locked door in this roo you can reach with a bit of hopscotch; pick it, and you'll have a clear path to le Roi des Thunes. Assassinate him.
Escape the Area
You're supposed to be sprinting for your life, but you're too cool for that. Use your Phantom Blade to kill off another Extremist from the group below you. Well done - optional challenge complete!
It's not easy to see your way around the sewers as you make an exit, but before you start calling Arno names remember he has Eagle Vision. All you have to do is follow your objective markers and kill any guards you come across; you'll see them before they see you. The mission ends when you reach the exit.