Sometimes they stay facing away and sometimes they patrol. Once you are ready to advance, keep an eye on the guards on the street. The buildings have guards too, but they are easily dealt with. This allows you to use the two side areas to avoid notice from the guards down the street. One will stay with his back to you, carefully take him out and his body makes nice bait for getting the drop on the other two in this area. Wait for the four guards to split up, you can get inside the guard shack while they talk.

Leave when you are ready and follow the tutorial to a street. When you are done, lock the door behind you and loot the rooms here. Carry him upstairs and leave him there for the moment if you want to loot the area. Simply knock out Ramsey if you want the bonus. In the throne room, hide to the right and wait until your target leaves. Be sure to move his body out of the room so your main target does not see it, killing the guard sometimes leaves behind evidence. Go downstairs and knock out the next guard. The key gets you back into the room you were just in. Be careful of the guard in the next room and take him out when he turns his back. Hop out of the window behind you and in another one. I chose Emily because her powers really help a lot with stealth. I played this in a “dead men tell no tales” fashion, which obviously voids a no kill playthrough.

I also would not recommend robbing any shops, the consequences later will make it hard to remain stealthy. Rule number two: Check your stats before you quick-save, it's a lot less time consuming to go back to an earlier quick-save than to restart the entire mission. That way you don't have to start over from the beginning of the entire game for one detection you did not notice until it was too late. Rule number one on this achievement: Save your game in a slot at the beginning of every mission.

Dishonored 2 mission 7 master key