Hitman Absolution Purist Difficulty Mission Guide: Mission 03: Terminus, Upper Floors

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This is the second part of the Terminus Mission in Hitman Absolution where you gain access to room 899 to listen to a conversation. This guide explains how to get through this part on the hardest difficulty, purist, without being detected and without killing anyone. This guide does not explain how to complete all the challenges in this area.
When you leave the elevator go towards the police tape but don't get too close to it. Let the employee pass.
When she is past you you can enter the room that is sealed by police tape (simply walk through the police tape). Go into the room to the right and sneak past the other employee. Before you exit through the door at the end wait for a few second before you exit otherwise the guard outside will notice you when your head sticks out. As soon as you are out of the room go to your left and hide behind the little section of wall.
Wait until the guard has looked into the corridor you are in and has turned around again. Turn around and approach the fire alarm and press it. As soon as you have go towards the chest of drawers near the alarm and wait out the guards that come out of the staircase.
Once they have all left leave the cover and go back through the sealed off room. When you exit that room be sure to crouch walk until you are a little bit outside of the room. I had a spanner from an earlier part but if you don't, and you will need something to throw later, there is a vase on the counter you walk by now. Approach the door to the staircase, but once you get near it hug the wall to the left as closely as possibly and go through the door keeping as far left as possible.
Once you are in the staircase keep hugging the left wall until you are well up the stairs. When you get to the top you see a door. Go into the door into a room with 2 guards. Crouch walk as fast as possible to the door to the right, the guards won't notice you sneaking by. When you leave that room.
Crouch walk as far left as possible so that the guard at the end of the corridor in front of you doesn't notice you. Immediately approach the half wall in front of you. When you are behind it walk around the right edge and take cover at the far right end of the half wall.
Wait out the conversation of the guards who will eventually leave. Once they have go to the other half wall near the seated guard in the image above. Hide on the side not facing the elevator. When you are there throw an object into the back right corner of the room.
A guard will come out of the corridor to the left of the elevator. As soon as he is a little bit into the room crouch walk around the right side of the half wall and into the corridor the guard just came out. The door at the end of this corridor is room 899. Walk up to it without delay and start lock picking it. Whilst you are repeatedly press the action button, E if you are on PC (which is used to activate stuff around the place), so that you get into the door as fast as possible because you just have enough time to lock pick the door before the guard you lured out turns around and sees you. When you are in room 899 go into the ventilation vent to the right of the door.
Make your way along it until you get to an opening. Here you can listen to a conversation. Once it is over make your way towards the back end of the ventilation shaft and the mission is done.