This is the second part of the Dexter Industries Mission in Hitman: Absolution which is called the Old Mill. In it you sneak around an old mill to get to the exit. This guide explains how to complete this mission on the hardest, purist, difficulty. It does not explain how to complete the different challenges in this area.
At the end of this guide is a YouTube video with a visual version of this guide.
At the start make your way up the stairs ahead whilst crouch walking. A guard will be leaning on the door ahead. Sneak up to him and subdue him before he can leave the room. Hide him in the cabinet behind you. On the opposite wall is an electricity box that you can sabotage. Do so and hide back at the top of the stairs by taking cover on the wall and wait for one of the guards to come and investigate:
As soon as the guard is working on the electricity box sneak up on him and subdue him. Then go out of the room and across the walkway and down onto the main floor. On top of the video game console is some evidence, be sure to take it. To the right of the console is a gasoline can. Take that as well. Go back into the room that you sabotaged the electricity box in and throw the gasoline can on the walkway near the exit of the room:
A guard will come and investigate. As soon as he has turned his back on you sneak up to him and subdue him. Hide him in the crate behind you near the other wall of the room. Next sneak up to the guard examining the floor next to the console. Subdue him and hide him in the crate behind you. Then go back onto the walkway and pick up the gasoline can from before. Go near the railings facing the main room and throw the gasoline can onto the ground on the main floor:
A guard will come to investigate. As soon as he has turned his back subdue him and hide him in the same crate you hid the enemy who was examining the floor next to the console. Be sure to stay in the part of the main floor near the console, the last enemy will have made his way down and if you are in line of sight of him he will notice you. When that guard is examining the map sneak up on him and subdue him. Be sure to take the key card to the left of the map on the table and hide this last guard in one of the remaining crates. All you have to do now is make your way to the top of the mill by following the walkway to the top. Once you have gone through the door it is the end of this part of the mission.