Map 1[edit]
Thanks to aliens and a marine guy, you're free now. You have nothing in your possessions but your wristblades and a charge emitter. If you've played the marine campaign and read the in-game texts, you know why you have those items. Since your mask is also gone, you cannot zoom in and switch between different vision modes.
Note: You don't have cloaking device, energy sift device and medicomb device, so you cannot turn invisible and restore your health at any time. Try not to receive damage at all costs.
Switch to your charge emitter and look for a panel. Open it and hack the circuit. This will make an elevator available, so head in and ride it up.
You will find yourself in some sort of an observation post. You must leave through the only door but it cannot be open right now. Prepare your wristblades and hide nearby. When the voices behind the door will trail off, two guards will go in. Kill them as quick as possible.
Walk out to the corridor. The way right is a dead end with a guard which will most likely just deal you damage and maybe kill you if you're not careful. So turn left, open the door and head down the stairs.
Open the hatch, drop down and kill a guard who is standing with his back to you. If you drop too soon, you might have to fight two guards at once. If you wait until they finish talking, take guards one by one.
Follow the corridor, open the door and you will appear in a hall with a big window. Behind the window there are a few humans including Rykov himself. Sadly, you cannot reach them right now, so jump to where the big red light is flashing. It's between two pipes at the ceiling. Destroy the panel and hack the circuit.
Head down and through the door that can be opened now. Two guards are waiting at the end of the corridor. Sadly, sometimes they don't rush in and keep their positions instead. If they do, you cannot hide behind a cover and hit them from the back, you have to charge at humans.
No matter how you killed those humans, open the door and go in. There will be a scientist who is extremely easy to kill. Take a remote bomb from the medical cart. You can read a PDA if you want. All doors are locked, so look for a panel, open it and hack it. Two guards will rush in and attack you, so better use your newly obtained weapon to blow them up.
Go to the next room which is now accessible. The scientist there is an easy trophy but the main thing is that you can obtain a mask and a netgun. The mask allows you to use different vision modes and a scope while the netgun will be helpful against far-away targets that are hard to approach. You can also read a PDA if you like.
Get outside and turn left. The new door is open now and a guard is shooting you. If not, backtrack and pick up all the necessary items you've missed. As soon as you've taken the weapons and the mask, you will be able to proceed.
There's not much to say. Go up the ladder and to a big pipe.
Map 2[edit]
Go forward until you hear two guards. If you wait a bit, they will make a few steps allowing you to attack them from their backs. Anyway, drop down and look for two levers, blue and red ones. Pull them to make a boom. Take cover not to get killed by explosion.
Go through the newly-made hole in the wall. There are three dead bodies already, two of which can be beheaded for trophies. Other than that, there is nothing of interest there. Go through the door, turn right and you will come to a room with your stuff. Pick up a combistick and a field generator. Quickly turn it on to become invisible since three guards will attack you.
Go back to the corridor. You can make a leap and walk above the corridor but it won't lead you anywhere. Go ahead and you will come to a reception of some sort. You can read a PDA about Rykov's past and your previous acquaintance with him. Yep, it was him whom you were hunting in the predator intro.
Anyway, back to the walkthrough. Open the next door and you will come to a big lab. There are three scientists – easy prey. Go to the big bright circle in the middle of the hall and pick up a plasmacaster (shoulder cannon) as well as both energy sift and medicomb devices. Now you can finally restore your health and energy. By that time two guards will appear and if you're invisible, they won't spot you yet. Kill them as well.
Go up the stairs and press a big red button to open doors and go in. Head through the next door and to the corridor. Two humans will be heading from the left. You cannot avoid them, so waste them and go down the corridor until you come to a dead end. Make a leap up to land on a net above. There you must find a lid. Smash it and hack the microcircuit.
Go back down. Two scientists and a guard appeared in the corridor. After dealing with them search the rooms. One of them holds just two computers with some plot data. Another room contains a speargun to pick up.
Exit the room and turn right. After a few steps turn left and you will come to a hall with crates on the left and two big pipes above. Look at the double doors right in front of you. If they are closed, backtrack and pick up all the items you've missed earlier. As soon as you've obtained all the gear you need, double doors will open. Head through them and finish the level.
Map 3[edit]
Before jumping down look at the enemies. Two humans won't be a problem, but the turret will kill you if you land in front of it. Now as you have the arsenal, you can deal with those enemies from above before heading down.
When you finally leave the elevator, you will have to face a few synthets who can see through your cloak. Some of them are armed with miniguns and even rocket launchers, so stay sharp. When you descend to the lower level, walk clockwise if you want to destroy all the turrets. When you drop to the lower level (not to the floor), be careful with turrets since some of them are hidden behind crates.
As soon as you destroy the barrels near the armored truck, there will be a huge explosion and the truck will fall down. From now on the timer starts. You have about 70 seconds to complete the next task or you will be killed by a dropship. Now there are two ways to beat this level.
Go stealth: Destroy all the enemies but try not to destroy the explosive barrels. When you finally feel save, go to the ground floor and shoot the barrels. Wait for the dropship and jump on it.
Go dynamic: Destroy the barrels from the start. After a few seconds the dropship will appear. Turn on your cloak and run as fast as you can trying to avoid synthets and turrets.