Map 1[edit]
Prepare your weapons and use the box near some dead person. You will find smartgun ammo and nightvision device.
There is only one way here and that way is down. Look for an open manhole with a ladder down near a stack of crates. If you get close, music will change and about six aliens will jump on you.
Head into the manhole, open the door and you will see an alien egg, another one is near the opposite wall. An alien will charge at you from right, so don't lose your focus. In the room itself you can find smartgun bullets in a box and a few dead bodies. There are lots of dead bodies on this level and using them is a lottery. You can get useful items or you can get an angry chestbuster. It's up to you to use them or not.
You need to find a tunnel and follow it. As you move ahead, an alien will attack you. Two more aliens will spawn behind you, so be careful. When you come to a turn left, don't miss smartgun ammo and a first aid kit.
Eventually you will come to a flooded room with two ladders and a sealed door. The long ladder right ahead is a dead end. Nothing interesting there, so climb the left ladder. As soon as you do it, two aliens will spawn.
Eventually you will come to a T-junction. You need a right turn to progress, but you can also scout a left turn for a box with a lot of ammo and flares. Anyway, you're near a sealed door. Take out the torch and cut four bolts on the door. As soon as you cut one or two, aliens will spawn behind, so deal with them before finishing the door.
You're in another round room which looks like the flooded one you've been before. The ladder ahead leads to a box with flares and pistol bullets. There's only one door that can be opened, so open it, follow a short corridor and open another door. You will see a lot of alien eggs ahead. Destroy them all and head in. Look for a ladder on the left and prepare for a tough part.
Climb up the ladder. From now on aliens will constantly spawn. Once you kill one, another will appear until you complete the objective. So without further hesitation look for a ramp down. It's in the corner opposite to a ladder you climbed. Follow a dark and winding road until you come to a dead end. Voice over means you're in the right position. Open the lever box and pull the lever. Don't forget to open a box with a smartgun. As you pull the lever, run back and up the ramp. One of the locked doors is unlocked now. Open it and get in.
Map 2[edit]
You're in a set of corridors. Walk forward until you see a closed door. Don't forget to pick up ammo and health kit on your way. Walk in and you will find yourself in a stairwell. You need to get to level 3 but before that you must activate security system on level 2. To get there you must grab a part of broken ladder and pull yourself up. You cannot reach it from below.
Once on level 2, open the only door you can open there and get to some sort of a warehouse. On the left there is a door with a padlock. Use your torch on the lock to open the door. Open the lever box and use the lever.
Go to the far right corner of the room for a box with some goodies. From there turn back and jump to the middle level of the huge shelf. Walk ahead until you see some boxes. Jump on them to reach the topmost level of the shelf. You need to get to a control panel and pull the lever that operates the crane. This will also spawn three aliens right away.
When the crane is finished, head back to the path that's been blocked by crates earlier. Crossing the warehouse will spawn a whole lot of aliens, so get your weapons ready. Now you can open the door that's been blocked and get to a corridor which is very similar to the corridor you've started the level.
Move ahead dealing with foes until you come to a locked door. Your teammate will tell something about overriding the lock. Once you hear that, three aliens will appear behind you.
Wait a bit until the door is unlocked and head in. There you will find an ammo box. Head up the ramp. You can read a PDA nearby. Now down the ramp and to a lever that's been behind bulletproof glass earlier. Pull the lever to activate the security system and unlock the door.
Head back to the warehouse and exit it through its upper level. That's where you've used the lever that operates the crane. You're in the stairwell again. Go down to the 3rd level while fighting aliens.
You will come to another warehouse. There's nothing interesting there, just a bunch of locked doors. Right from the start turn left and try to open the door there. The lock will break, so take out your hacking device and use it as intended. Go to the gateway. If you turn back now, you will see a huge armored alien charging at you. Luckily, the doors will close shut before it can reach you.
Move ahead and kill two more aliens. The door at the end of the corridor is locked, so take out the torch and cut the padlock on a vent. The huge alien will run at you. You can't hurt it with your weapons, so quickly crouch and dive to the vent.