| NOTE - Make sure you save at least one Sleep Dart for near the end of the mission. You will need it if you want to take down Campbell non-lethally. |
When you land, head right and you'll see a guard with his back turned, as well as some on the bridge above dumping some bodies. Don't worry about the ones above, and sneak up behind the guard and take him down. You have some choices here on what to do next, as you can go and meet with Granny Rags, who has some errands for you to do. Or you could go and search for any Runes and Bone Charms, making sure to use The Heart to pinpoint their locations. Your goal for the main mission is to get past the two Walls of Light.
FIRST WALL OF LIGHT
There are a few things you can do to get past the first Wall of Light. There is one guard patrolling the grounds in front of the Wall of Light; you can take him down and remove the whale oil from the machine to deactivate the Wall of Light. You can also climb onto the crates to the right of it, then onto the roof to bypass the Wall of Light.
Whichever method you choose, you will need to find a way past the second Wall of Light after bypassing the first. There are more guards in this area than the first, with around 2-3 patrolling the area. Once again, you have some options on how to get past this second Wall of Light. You can hop over it by using the rooftops, take down the guards and removing the whale oil, disabling it, or you can use the Bottle Street alley to get past it.
SECOND WALL OF LIGHT
If you take down the guards, be careful since there are more than one in the vicinity, hiding their bodies down the stairs on each side. There are two patrolling at first, on opposite sides, with another joining in if you get close to the Wall of Light. Once all the guards are knocked out, go to the machine and take the whale oil out to disable the Wall of Light.
Alternatively, you can get over the second Wall of Light very easily via the rooftops. On either side of the area are balconies, one side leading to Galvani's place, with the other side being locked up; you want to go on that side. Use Blink to get to the top balcony, then Blink again to get on top of the sign towards the Wall. From there, you can just barely make it onto the roof above the Wall.
The last way you can get past the second Wall of Light involves going through an alley where the Bottle Street Gang is located. One of the side stairs in the second area leads down to an alley, where you can find a gang member alone, so take him out and go into the alley he was guarding to find three more members arguing. One of them will be killed in the scuffle, but you don't really need to take out the other two, as you can wait until they reset into the middle area, then use Blink a couple of times to get past them and get up the stairs.
Once you get past the second Wall of Light, use Blink to get onto the vents on the left side of the area. There are at least two guards patrolling this area, one of which will go inside the trailer-like structure. Take them out when you get a chance, or use the street lights to wait until they get away from the door to Holgar Square.
HOLGAR SQUARE
When you first arrive in Holgar Square, you will see one guard in front of you, with his back turned, questioning someone that is locked up. This is Martin and he needs to be rescued, so quickly sneak up behind the guard and take him out, then flip the switch to the left of Martin to free him. He mentions that Campbell is meeting with Curnow, and that he plans on poisoning him (which we don't want if you want to save Curnow).
Once you're done talking, climb the boxes to the right of the gate and scout the area. There are two guards talking near a door, one of which will start patrolling the area once they're finished speaking, and there's already a guard walking around. You can take down the guard closest to you while the other two are talking, then take down the other when the chance arises.
Once those two guards are knocked out, approach the door on the left side and look through the keyhole, waiting until the guard inside starts walking away before opening it and taking him out. Peek through the keyhole of the door on the opposite side, waiting for the guards to not be looking in its direction, then open it and use Blink to go down the stairs.
While there is another option to get inside the Office of the High Overseer, going down the stairs and through the sewer pipe is the easiest and best one. Climb up the chain, then go through the door and you'll see two doors and a window you can climb through. The door to the right leads to the Kennel area, which is completely unnecessary and doesn't have any Runes or Bone Charms, so there's really no reason to go there. The window and other door both lead to the same area, the Office of the High Overseer.
OFFICE OF THE HIGH OVERSEER
At the top of the stairs, you will see a courtyard area, complete with some stairs straight ahead, and the front door to your left, farther away. There are a few guards in the area, one or two walking around near the front door, and at least one walking around the courtyard. When you get the chance, hide underneath the steps straight ahead, then go straight ahead to the right of the main entrance, where you can find a window to crawl through.
This small passage only leads to a grating, where you overhear two guards talking about Campbell's journal; that room is Campbell's Secret Chamber, which will play a role later on in the mission. Go through the other window directly across where you entered, and you'll be right by the front door. Scout the guard(s) patrolling in front of the door, then go in the doors, making sure to close them behind you.
When you enter the building, there will be some enemies across the large room talking, as well as two side rooms that lead out to small hallways that access stairs that lead to the second floor. There are guards that come by the side rooms on both sides, so be sure to knock them out and hide their bodies well. It is important to note that the guards talking in the big room can spot you in the short hallways, so use Blink to stay behind the pillars and get into the stairways.
Of utmost important is the eastern stairway, which has a door leading downstairs. You can see a statue of Halgar with a colored eye down here; if you press this, a secret door will open up leading to Campbell's Secret Chamber. Later on in the mission, you'll need to quickly make your way to this stairwell and get to the secret room. You'll want to knock out and hide the bodies of the guards on both sides; if you can't hide the bodies too well right now, you can do a better job in the next section.
TO THE MEETING ROOM
In order to take care of the High Overseer in a nonlethal manner, you will need to do some extra legwork. You need to head to the Archive or Interrogation Room to read instructions on how to cast out Overseers. If you read it in the Archive, you will still need to head to the other room to get the Heretic's Brand tool, so it's just better to head to the Interrogation Room to begin with.
There are quite a few guards roaming the hallways up here on the second floor. You might have noticed some pipes running along near the ceiling; this is a great hiding spot for the bodies of the guards. There's two roaming around near the east stairwell, and two more talking outside of the Archive, who split up and walk around after finishing. There's another guard inside of the Archive, reading up on Corvo on the second floor.
Before going into the Meeting Room, do another round of the premises and make sure you got all the guards, doubling that you have them all secure on the pipes if you chose that method. Also, it is wise to open up the secret door to Campbell's Secret Chamber, as this won't slow you down when hurrying here afterwards.
Go inside the Meeting Room, either through the door or through the window above the door. When you get inside, you'll notice a bottle of wine and two glasses on the table. Press the <Action Button> on the glasses until a choice shows up on your screen, which either lets you poison Curnow, poison Campbell, or spill the glasses. You want to spill the glasses, so choose that and then use Blink to get onto the pipes in the room.
BRANDING THE OVERSEER
As you're waiting on the pipes, Campbell will step into the room with Curnow in tow. Campbell will make some comments about the glasses being broken and suggest to Curnow that he follow him to where is storing some more wine. This is your cue to get out of there, and start heading your way down to Campbell's Secret Chamber. You might want to wait on the stairs going down, just to make sure that Campbell and Curnow are moving, as they've been known to stop sometimes.
When you get to the Secret Chamber and if you haven't been here before, take the Sokolov Painting, which will help a little in a bit. Hide along the wall, to the left of the door and prepare your Sleep Dart. When the pair enter the chamber, Campbell wonders where the painting went and tells Curnow to search for another. As soon as Curnow turns around, Campbell will take out his sword and stab Curnow. So, as soon as Curnow turns around, shoot Campbell with a Sleep Dart and hide in the little space ahead of you provided by the boxes, as Curnow will simply walk right out of the room.
It is suggested that you wait, monitoring Curnow's position by his objective marker, until you get confirmation that he has been rescued, which fulfills your optional mission with Callista back at The Hound Pits. Pick up Campbell's body and start heading towards the Interrogation Room, being extra careful if you missed any guards or any extra come out of hiding.
When you get to the Interrogation Room, place Campbell into the chair. If you didn't get the Heretic's Brand tool before, get it now and use it on Campbell. He is now marked and will be excommunicated from the Abbey of the Everyman.
THE ESCAPE
As soon as you brand Campbell, your job is done and you need to escape. Head out of the room and go down the stairs closest to you, exiting out the marked door to the Back Yard area. If you didn't go to the Kennel earlier, this is your first run in with the Wolfhounds, who are patrolling with the Overseers. It is best to leave these alone, as you don't really need to do much back here except get to Samuel.
Use Blink to get across the rooftops of the buildings here. If you want, use The Heart to try and get the Bone Charms and Rune in the area before leaving. Keep going across the the rooftops and the pipes until you get to a chain leading down to Samuel, so climb down it and talk to Samuel to get out of there.
