Rewards: Pounds: 3990 (+250), EXP: 4500 (+250), Schematic: Legendary Assassin Belt Schematic
Challenges: 1. Free all captive royal guard groups. 2. Use a key to enter the White Dragon Room.
This is the final story mission. Follow Jacob into the backyard. Scan the area and kidnap one of the guards marked red when they're far away from the other guards. Head back inside, go through the first room and pass inbetween the two guards so you can head upstairs. Don't release the guard just yet, but continue down the hall and enter the room at the end, then turn left. In this room, feel free to finally strangle the guard. Loot the nearby chest, check the table in this room for a Letter (also see the minimap) and open the door to find the chest with the plans. Continue through the next door (ignore the one to the side, since it only leads to the main hall and there are guards behind it) and proceed to the room at the far end to find another chest. Head back downstairs via the main hall, but only when the guards there are looking away.
As Jacob, climb to the roof of the building and approach Abberline to get your Assassin outfit and weapons back. Defeat the six snipers, then proceed to kill the 16 impostors. There are two groups of imprisoned guards, tied to eachother with rope. They are marked green when you scan the area with Eagle Vision; release them to complete the optional objective. One group is held in a small alley (there's a Letter there too), the others close to where you killed the snipers (it's good to start there). You can also find a Letter in the corner of this area.
After several scenes, make your way to the vault by swimming to the other side. Inside the vault, slide down and follow the linear path until you reach Starrick. At this point you'll switch back to Evie, who has a little less than four minutes to save Jacob. Snatch the Letter along the way before you take a swim (check the minimap) near the group of people, then make your way to the vault and defeat a few Templars on the way. Inside the main vault, approach Starrick.
This is made a little more difficult by triangular laser beams, but the first time around it's not at all hard to dodge these. When you get hit, you suffer some damage and are temporarily stunned. There will be somewhat more difficult laser beams in the next few phases of the fight, but the main way to get past them is to rope launch to higher ground, be on the move, and lower yourself again or shoot rope close to Starrick. Sometimes you just might want to not bother and brute-force your way through the laser beams. As long as you have some medicine, this is actually quite a fast method.
When you reach Starrick for the first time with Evie, attack him fiercely. He'll enter a (counter-)attack mode at some point, at which you should carefully time your counter his attacks just before he launches them, at the moment his health bar turns yellow. During the regular battle, don't bother using knife or pistol attacks, since they don't hurt Starrick. Keep on punching and slashing until a scene is triggered.
As Jacob, rush to Starrick by going via the side, then pummel him some more. As Evie, dodge the lasers by using the rope launcher and pummel Starrick afterwards. As Jacob, either use the rope launcher or brute force your way through the lasers and rescue Evie. Continue the fight after the scene and you'll soon be able to land the finishing blow. Congratulations, you've defeated the villain of the game whom you've only just met!