As before, switch to thermal vision - no aliens here. Go forwards through the door and then into the room at the far end of the corridor, on the left, kill any marines there may be in there and destroy everything, except for the field charge which you should find. Pull the lever, then exit the room and continue down the corridor. When you reach the door that doesn't open, look left and hit a switch with a small arrow on it. Proceed through the now open door and the lift will take you up. Exit it and follow the path round to the left and down the several sets of steps. When you reach the bottom, head right, then left into the large open area, then left again and follow the path round. Eventually you'll reach a door, which opens to reveal several barrels. Kill any humans present and then cloak yourself, switching to Speargun. Lean over the edge and dispose of the guy at the bottom (on the right). When he's dead, fall down to where his body is and collect the security pass nearby. Then catch the lift back up and follow the path back round to the bottom of the stairs. On the left, at the end of the corridor, is a vent that you need to smash. Do so and enter it. Smash the identical grate at the other end and enter the lift across the corridor. When you reach the top you will enter another control room. Again, destroy everything, pull the lever and collect the field charge. Exit via the other door and follow the corridor round until you reach the end. From here you can now jump onto the bridge. Head right, follow the corridor round and go through the door. You're now in some sort of meeting room. Head straight across to the door on the other side. Head down the stairs. After 3 sets, there's a door on the left. Head through it to collect some field charge and open a door; but it's somewhere you've already been, so head back to the stairs. Continue down another 2 sets until you come to another door, this time straight in front of you. Go through it and read the message. Yes, you have to jump that gap, just try to get the timing right. Save just before you jump if necessary. When you get across to the other side, go through the door. Head left, then enter the door on your right. Another control room, so usual routine - smash all, hit lever, grab field charge. The lever unlocks all the doors, so now you can progress into the building. Head back out through the door you used to enter, then go left, follow the corridor down, and take the second left. This takes you to the kitchens. Go left, across the room and through the door. Now walk around the back of the sentry gun and take it out with your wristblades. Head around to the right and through the door to enter the mess hall. Continue through it and the door at the end. Take the left turning and go through the door, but don't go around the corner just yet. Cloak and ready your Speargun. Shoot the marine(s) at the end of the corridor and walk towards their bodies. When the door closes, take a right. Fall down to the floor and enter the vent to the right of the bookcases. This takes you to the laundry room. When you get there, smash all the containers (the washing machines on the right are indestructible) and you should find a laundry chute in the far left hand corner. Fall down it, then smash the grate that is exactly opposite the one you just exited (you'll have to stand on one of the containers), and enter the vent behind it. Continue through this, smash the grate and enter the hangar. Kill any marines present and enter you ship via the ramp at the front of it.