As you begin the mission, look on the bar to the left for a Diary Note [Note 1/2] .
Note: For finding the first 10 journal pages, you will unlock Achievement/trophy ‘First Draft’.
There is also a lockbox containing a tidy sum of ammo for your weapons on the bar near where you found the diary page. Head over to the other side of the room and grab a mask and Filters from the box your friend opens on the table. There is also some ammo and a Medkit here as well if you desire it. Follow your mate through the door.
Work your way under the stairs and around the back of the dumpster there to find a hole in the wall. Inside is a safe containing ammo and +50 Military Grade Rounds . Return and climb up the stairs to find yourself on the surface.
When you are back in control, look back towards the stairs you came up. Just to the left of these is an open doorway. Inside you’ll find a corpse that you can plunder for another Filter . Follow your friend over to the far end of the rooftop and walk down the wing of the plane after him. Keep on his tail as you work your way around a hole in the ground towards another subway entrance in the distance. Before entering this, look to the left to see a small hole in the fuselage of the plane up the small hill nearby, if you head up here you can find another Filter . You’ll also get a Morality Point for your trouble. Return and enter the subway.
Follow your friend into the next room and loot the corpse he points out on the ground for some ammo and a Filter . You can also change your Gas Mask if you wish to do so. Check out the small room on the right for some ammo and a Morality Point . Continue onwards until you reach the stairs on the left leading back to the surface. Enter the small service passage to the right at the base of the stairs.
Grab the ammo from the corpse in the tunnel and in the room at the end, loot the lockbox on the table for some ammo and a Medkit . Grab the custom weapon front the table for a scene. Afterwards you will earn a Morality Point . Return to the main area. Turn off your torch and climb the stairs. As you near the top, your friend will tell you to stop. Crouch and sit next to him and wait for the enemies to pass.
For allowing them to pass and not being spotted, you will earn a Morality Point and an achievement/trophy.
Note: For letting the watchmen pass without shooting at them, you will earn the Achievement/trophy ‘Mouse’
When the coast is clear, follow your team mate over to the crashed plane and interact with the door when requested to do so. As you enter, turn to your left and grab the Filter from the ground at the dead end. Return to the door and follow your friend to the through the plane until a scene plays.
After the scene, walk towards your comrade and look on the ground to his left for Diary Note [Note 2/2] . Grab this and then approach your friend for a scene. Listen to him after you save him for another Morality Point .
Once he is back on his feet follow him back through the plane. Loot the corpse propped up against the right hand wall for some ammo and a Filter . As you exit the plane a demon will attack you so help your friend take it down.
Once it is dead, look over to the left from the exit of the plane to see a bus and some cars. Below these is a corpse you can examine for a Filter . The closest building to this has an open door. Inside behind some pipes is another corpse you can loot for a Filter and a lockbox containing ammo and +5 Military Grade Rounds . Exit to the main street and follow your friend.
As you approach the next corner a large group of watchmen will appear on the top floor of the building in front of you and drop down to attack. You will have to fight off 7-8 of them. Once they stop coming, quickly follow your friend around the corner and approach him as he stops to be boosted up into a building.
When you regain control, look to the left of the nose of the airplane in here to find an escalator leading down. Run down to the door at the base of the escalator. Turn around and kill the watchmen as they come down the escalator towards you until a scene plays to end the mission.