Follow him to the right. He’ll stop you in front of a room with an elevator. Once it goes up, follow his instructions and use the shadows to cross the room to the tunnel on the far side of the room. After a brief examination of the gate, your new friend will ask for a lift. Approach him to pop him up to the raised ladder nearby. He will lower a ladder for you. Follow him up to the upper platform.
Crouch and move after your friend along the wall to the left. When he points out a target to you, drop down to the platform on the right and sneak up behind the guard. Take him out. Next, hit the lever here to lower a set of stairs leading up to the next level. Climb the stairs and unscrew the light at the top.
Wait for your friend to disable the light over the centre of the room and then look across the bridge. Wait for the guard to patrol to the left and sneak across the bridge, get up behind him and take him out. Climb the ladder. Enter the circular pipe at the top of the ladder and head through until you reach the far end. A scene will play and you will drop down to the room below.
When you are back in control, loot the other Throwing Knives from the corpse on the wall and look in the alcove opposite. There are crates here and on top of one of them you’ll find a Diary Note [Note 1/1]. Behind the crate is another Throwing Knife.
Sneak up to the open door leaving the room and wait for the guard to look away from you. Sneak up and take him out. Turn the lights off here to hide the body. Climb the stairs here and at the top approach the large door. Use a throwing knife to disable the light above the door and then hit the green button to open the door. Quickly run over and hide behind the crates to the right of the door.
Wait for the guard to walk into the room and look over the centre of the room. Sneak up behind him and take him down. Go through the door and hit the lever in here to open the next door. Once it opens go on through and disable the light on the right.
Follow the right hand wall up the stairs and wait for your friend to eliminate the guard walking down the stairs on the far side of the room. Continue following the wall and duck into the alcove on the right. Climb the ladder here and follow the catwalk around the corner to the right. Wait for the guard ahead to start walking away from you before sneaking up and punching his lights out. Continue to the very far end of the walkway here and hang here for a moment.
Wait for the patrolling guard to enter the room to the left and inspect the crates along the wall. Drop down behind him and take him out. Exit to the main room and enter the adjacent room to the one we dropped down in. Take out the guy in the chair. Exit to the main room, cross the water and climb the short set of stairs opposite. Punch out the guy standing at the desk in front of you and look to the right. Do the same to the seated guard near the window.
Now that the room is clear, pull the lever on the desk next to the final guard to release the prisoners. Doing this will give you a Morality Point and an achievement/trophy.
Note: for freeing the prisoners you will unlock the Achievement/Trophy ‘Freedom!’
Head over to the door leading to the next area and use the lever to open it. Head on inside to the next room to complete the chapter.