OBJECTIVE: Locate and Kill Paxton Fettel
You'll find yourself in a small room. Go to the door, open it, cross the bridge and approach the ladder. Go down and then keep walking the only available path to the next room.
There's nothing interesting in here, thus turn right and walk down the corridor till you get to the hall with an empty canal. Go down the ladder and go left.
You'll get to a technician's corpse and you'll find a VK-12 Combat Shotgun and two N6A3 Fragmentation Grenades next to him. Return to the canal, go up the ladder and cross the metal bridge. Then go right and up the stairs.
Cross the metal bridge to get to a room. Inside you'll find an AT-14 Pistol on the shelves. You can also listen to the voice mails - the phone is on the wall. Go back to the stairs, go down and turn right.
Keep walking down the wide corridor until you get near another canal. Go right, go down the ladder on the left and then turn on your watch and go left. On the left there's an entrance to the ventilation shaft. At the end of it you'll find a Health Booster. Take it and go back to the ladder. Go up, turn left and keep walking down the corridor.
Keep going forward along the generators. Turn right, go downstairs and come to the door on the left. Then, go forward in the corridor with the pipes until you arrive in the world of visions. You must continue going straight on to the door from which the voices are coming.
When the door disappears, turn around quickly and try to shoot a demon (the demons are flying straight into you, by touching you they take your life and disappear - your chances to make it are very low, so in case of losing, don't worry). Go to the end of the corridor and you'll be transported back to the real world. Open the door and take the Medkit from the shelf on the right.
The door on the left is blocked but you can break the metal plate down and enter the ventilation shaft. Go to the very end and break down another plate near the short stairs, save your game and approach the corpse "sitting" on a chair. Don't worry - the dead one won't wake up. Soon, however, soon you'll be in trouble.
Hide behind two blue pipes, just as it's depicted in the picture on the left above, and wait. Now, it's getting really tough. The lights will go out for a short while, soon afterwards a couple of soldiers will run out. You must be extremely careful now - not only you'll be surrounded, but also your enemies will be at the higher positions. Remember to lean out repeatedly and use Slo-Mo. When Slo-Mo ends, just wait until it reloads. You shouldn't get much damage from the adversaries' grenades provided you hold your position.
After you've killed all of them (about five or six), leave your hiding spot. Take the Medkit and a G2A2 Assault Rifle from the first box and a Body Armor from the other. If any of the soldiers' weapons has fallen on the ground - pick it up (all were carrying RPL Sub-Machineguns). Go to the corridor on the left. On the way kill a soldier who's got a VK-12 Combat Shotgun (if you still have enough Slo-Mo, you'd be able to take him by surprise).
Take two AT-5 Proximity Mines, which are on the left, and go right. You'll get to a room with metal shelves, there's a Medkit on one of them. Watch out - there are six soldiers on the right (three G2A2 Assault Rifles, one VK-12 Combat Shotgun and two RPL Sub-Machineguns). Let them see you - now, either go back, hide behind the wall, remain hidden, lean out and kill any enemy you see running out ...
... or attack them yourself by, first, shooting at the shaking gas valve on the right, which will cause a huge explosion. One way or another, after you've killed all the adversaries, pick up their guns and go to the short staircase. On the left there's a pathway but for now omit it and go up the stairs.
You'll get to a room with blue gas bottles. On the box there's a Body Armor. There are two ways out of here but you should go back to the exit you've previously omitted. You'll get to a room with the technician's dead body and a ladder. Climb it up.
Next to the body you'll find an AT-14 Pistol. Jump over the yellow rail on the pipe, turn yourself to the left and break the metal plate down. Enter the ventilation shaft which will lead you on the pipes. Walking on the pipes, you'll get to a small room with two M77 Remote Bombs and a 10mm HV Penetrator.
Go left and jump on the pipe which you can see in the picture on the left above. It'll lead you to a ventilation shaft where you'll find a Reflex Booster. Downstairs, in a big room there are five soldiers. Three of them have RPL Sub-Machineguns and two - 10mm HV Penetrators. Choose some accurate weapon, lean out, use Slo-Mo and kill them one at a time. The chances for any grenade ending up in the ventilation shaft are low, but should it happen - you can load the game at once.
Once nobody stand in your way, jump down, go straight, and take the Medkit that's on the left. On the right there's a pathway leading further but now you should omit it and turn left. Go to the door depicted in the picture on the right above.
You'll get to an L-shaped room, exit through the door and take two N6A3 Fragmentation Grenades and a 10mm HV Penetrator, which is against the wall. Next to it there's a Medkit on the yellow barrel. Keep going this path till you get to the room from where you took a Body Armor - turn left and you'll come to the huge hall where you killed your last enemies. Pick up their weapons and go through the entrance you've previously omitted.
The corridor will lead you to the place where you'd be able to either go in through the open door or turn left. Choose the door and take the Medkit from the wall. Then, go back to the corridor and keep going further.
Get your weapon ready and move forward with care - in front of you, next to the pillar two soldiers armed with RPL Sub-Machineguns will appear. Kill them and turn left, walking on a metal bridge you'll get to a small room with a VK-12 Combat Shotgun and a Body Armor. Go back to the corridor and pick up the dead enemies' weapons on the way.
Behind the big box you'll meet another two soldiers who carry RPL Sub-Machineguns. Kill them and go round the place where you found the corpse on a chair. Collect the weapons from the adversaries you've killed before and go near the blue door.
The entrance is on the left - you need to crouch to go through between the pipes. Once you get to the very end, jump down on the metal bridge. You'll go to the next stage.