When the level begins, switch to thermal view and smash the glass. The door opens, so go out and kill all prey. Proceed through the set of doors below the "Welcome to Gateway" sign. Fall down and smash the vent, then go through the doors. The alarm starts going off. Smash the glass and run to the end and then through the door to the right. Fall down into the dock below, then smash the power modules on each side. Switch to electrical view. The door at the end opens, revealing a sentry gun and an open vent. Aliens emerge from the latter, but get splatted by the sentry gun (some make it past, so be prepared to take them out). When the aliens stop coming, smash the sentry gun and pull yourself into the vent. When you reach the other end, drop down and go to the middle of the corridor, where there are some barrels. Doors open either side of you and behind them are power modules - break them. The fans above will stop, so use your grappling hook to pull yourself into the vents. Make your way into the large area ahead, and kill the Praetorian. Then, take the middle vent and follow it round into a room containing a marine with a flamethrower. Kill him, then go over to the pipes on the far side of the room. Crouch and walk under them, then fall down to the area below. Proceed through the two doors, behind the second of which is a minigunner. When he's wasted, pull yourself up into the hole in the ceiling, then continue going straight up - going along offers nothing but large numbers of aliens. When you reach the top, proceed through the two sets of doors and fall down, then smash the grate, fall through and break the glass. Jump over to the computer and break it apart - this causes the door to open. Go through it and fall to the floor of the dock. Watch it - on the other side is a Smartgunner. Take him out, use your Medicomp and collect the field charge. If you have a save left, I'd strongly recommend you use it now. Break all the power modules, making sure you're in thermal view, then cloak and hide in one of the power mole areas. The doors at the end have opened, and behind them are the commanding officer that you have to kill to end the level, and a minigunner. Select the Speargun, then slowly crawl out until you can see half of the minigunner's body, then kill him and do the same with the commanding officer. End of level