Now that you've taken care of the side missions with Granny Rags, it's time to focus more on the main quest to take care of High Overseer Campbell. The only entrance to the Overseer's compound is through the front door, so you'll just have to avoid the enemies in the underpass. Slink under the pass and approach the door. Use the Heart before you enter the Overseer's base to find a Rune by the City Watch kiosk just past the Wall of Light.

Enter the compound when you are ready. Overseer Martin is an ally of the conspirators, and should be rescued in this area. It's not a necessity, but you should do it to get completion. Choke out or kill the guard by Martin, and then use the lever to free him. He will open up the base for you. Now you can enter the base proper. You can use Blink, especially when combined with Agility, to bypass the majority of the base altogether. If you are not fortunate enough to have both abilities, or if you are playing a less navigation-focused build, sneak or slaughter your way through the compound and towards your waypoint. Along the way, keep an eye out for goodies like potions, coins and ammo.

You will stumble upon a door leading down to the kennels along the way. This area is entirely optional. Don't go down here if you're looking to get Ghost, because there isn't much of worth here and you'll almost definitely be detected. There is a locked door down there, though, that leads to some pretty good stuff. The combination to the door is 217. Open it to find Campbell's secret room. Open the door. Directly across from the door, you will find a statue's head. Press the left eye of the head to open the chamber. Inside of the chamber you will find another Rune. A Sokolov Painting is in this room as well.

Now that you've looted the kennels, you have another optional objective to contemplate. You can discredit Campbell instead of killing him, but you'll have to do some reading. In order to get the non-lethal version of this mission, you'll have to head to the Archive or the Interrogation room and read about the branding process. Once you have the branding instructions in your possession, take the brand from the interrogation room and clear out a path through the guards on the second level of the compound. You don't have to kill them, but you will want the coast to be clear since you'll be dragging an unconscious body around in a minute.

Enter the meeting room where Curnow and Campbell are talking. This will trigger a sort of invisible timer, giving you only a few seconds to decide how you want to handle the situation. If you want to take a less lethal route, waste no time in hiding. Head underneath of the table where the wine cups are to stay out of sight. Under the table, you can pickpocket Campbell's journal while he talks. You can save Curnow by interfering with the wine before the pair makes its way into the room. Switch the glasses or spill the wine, depending on whether you want to kill anyone or not, to save Curnow. Poison both glasses if you just want to be a dick. If you're dead set of saving Curnow, note that it's helpful to rewire the security systems on this floor of the compound, just to make sure that he doesn't go getting himself into trouble.

Now that you have Campbell's journal, one way or another, you can feel free to abandon the area. Sam's boat will be in the backyard area. There's still some stuff in the compound that you won't want to miss collecting, though. Blink past the door to avoid being detected by guards, and proceed towards your waypoint in the backyard. This will lead you to the Overseer workshop, which has tons of stuff for you to loot. Use Blink to get up onto the roof, and enter the building through the skylight. You can find the Bonded Galvani Weave in the workshop, as well as a Rune on the workbench. Also be sure to grab the seemingly random valve wheel from the ground and carry it with you as you near the exit. Near the extraction point, you will find a closed shutter just begging to be reattached to the valve wheel. Stick the valve wheel on the pipe protruding from the wall and hold the action button to turn it. This will open the shutter door, but only for a very short time. Sprint and hit crouch to slide under the door before it closes. Inside of this secret room you will find two Bone Charms. The first will be directly inside of the room, while the second will be in the next warehouse. Use Blink to get on the roof and follow the Heart inside to find it

There will be guards in this area, so you can't simply run amock. If you find that the guards are giving you too much trouble, you can take care of them without getting your hands dirty. In order to do this, drop down and choke on of them out. The bowing guard is the best for this. Then, let the other two perform their little procedure before choking out the killer. There is a safe nearby containing some Sleep Darts and coins. The combination is 203. Punch it in, loot the safe, and head over to Sam to leave the area.