This is the last part of the Rosewood Mission which is called Central Heating. In it you go after Wade and eventually eliminate him. 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.
When you start go to the left side of the cover yo are in. Pick up the bottle and go around the corner whilst staying in cover and go the the other edge of the bed. Wait until the enemy in sight starts talking, then press the button to change cover. Once the enemies have stopped talking throw the bottle you picked up onto the other side of the room as soon as the enemy with the mouth mask is past you:
Keep an eye on the enemy with the mouth mask. As soon as he has turned away crouch walk through the door out of the room. Follow the corridor until you see an enemy smoking with the back turned towards you. Walk up to and take cover behind the stack of stones to the right side of the enemy:
He leaves shortly after you have taken cover. Follow him until you can jump up to a ledge. When you are on the platform take cover behind the sold railing directly behind the pillar. Look down and wait for the enemy with the face mask to turn around and walk away:
Then follow the platform and make your way over the bridge. Take cover on the first solid railing. Move the the left and change cover as soon as you get to that cover. Wait until the enemy ahead has walked forwards to stand at the top of the stairs:
Sneak towards the exit of this area and follow the corridor and go through the door at the end. Once the cut scene stops make your way down the stairs onto the lower platform and then down the next small bit of stairs. Then go towards the boilers:
Turn the wheel ahead to turn off the steam pouring out over the air ventilation shaft. Go into and follow that shaft to the other side. Go around the various pipes and boilers until you find another wheel: