Objective: Get to the end
You arrive at one of Troy Colony's main gates...
Your first job is to take out the aliens with the help of two friendly marines. Once all is clear, use switch 1 to open up the gate. After using the comm terminal and the pattern buffer, approach the door at the other end of the corridor. Be alert, because once you get close enough to the door, large groups of aliens will come out of hiding and attack you.
After dealing with them, you'll notice that the door does not open manually but needs to be opened by switch 2, which is located in one of the secret areas the aliens were hiding in. Once the door is open, flip switch 3 behind the pillar, which in turn will open door C.
Cross the path between the lava pits, but look out for the exploding Boomers hidden in the lava. Switch 4 is adjacent to the room you are now in; flip it. Door D will open, allowing you passage to a lava river with a room containing 6 switches on the other side of it. Only the right combination for the switches will open the doors to the east. As you stand facing the six doors, flip the 2 nearest switches on your right and the middle switch on your left. This will open every door, but note that the furthest door closes automatically after a few seconds. You can re-open this door by flipping the middle switch on your left.
Switch 5 is in the room beyond the 6 door puzzle - flip this before leaving by the lift. This will open door E, allowing you access to switch 6. Head back to switch 6 via door D again. Trigger it to open door F, which leads to switch 7 (opens door G). Now go to switch 8, which will open a heavy door (H) into a small storage room. Go through door G, and flip switch 9 to open door I.
The rest of the level is easy. After visiting the recharger, use switch 10 to open door J. Drop off the ledge and quickly use the pattern buffer, but don't forget to take out those monsters first. Flip switch 11 and wait till the large platform K to the east is at ground level. Flip the switch again then run to the platform and get on before it rises. You'll be carried up to the final comm terminal, which will transport you to the next level, Command and Control...
