Setting	00 Agent
Target	2:05
Cheat	Invincible
Achieved	2:00

This is one of the trickiest cheats in the game. This'll take a lot of practice and a lot of luck too - you can end up doing a perfect first half of this level only to come unstuck when Dr. Doak is not in the right place. There's a few guides to this level out there, with minor variations. This is how I managed to finish it, but its not the only way. The main difference to the guides is on use of remote mines.

Hints: Dodge in and out of arches to avoid taking hits. Try and shut doors as you go through them if you're not coming back, but don't slow down to do this, just think of it as a bonus as it'll take the heat of you by slowing down the pursuing guards. When you're waiting for metal sliding doors to open, duck to the side to avoid getting shot in the back.

You start in the airshaft. Head forwards and take the turn to your left. Head down here, turn the corner and drop through the hole. By now, you should have armed yourself with a remote mine.
You're in a cubicle, open the door, head out and angle left towards the next door. Go through this and the next door immediately on your right. You're now looking down the stairs.

Head down the stairs and throw a mine to the right of the door in front of you, onto or near the stack of crates to the right of the door. If you get it too close to the door, you'll blow the control inside this room. At the bottom of the stairs, turn 180 degrees to your right and head through the door under the stairs. As you do this, press A + B together to blow the mine, then hit B three times to arm the PPK. Head through the door and shoot the guard, and grab his KF7 and the keycard. Do a u-turn and head back through the open doorway, arming the KF7 as you go. Head straight ahead and through the metal door, which may or may not be open. You'll be getting shot at but ignore it. Inside here is the remote door control, activate it. If its blown you'll need to restart.

Head back out the door and head left. There'll be some smoke but you should now this level back to front, anyway :) At the bottom of the corridor turn left and open the door at the crates. While it opens, duck to the right and then head through the door as soon as you can. Turn the corner to the right and head through the door which will have be opened by the remote control. Charge straight forwards and open the metal door in front of you. Once you go through this door three guards will be advancing, shooting at you. Run straight through, shooting at them as you go to slow some of them and strafing to avoid flying bullets. Open the door at the end of this corridor, duck to the side while it opens to avoid some bullets and go through as soon as you can. Try and shut the door as you go through to take some of the heat off. Open the door directly in front of you, again, duck to the side and then head through the door as it opens, again trying to shut it as you go.

Turn to the left, head forwards and then turn right. There'll be a soldier walking away from you, before or after you get to the corner. Either way, shoot him. Straight ahead there's a door. Another soldier'll pop out from behind a pillar on the left, shoot him too then hide in front of the pillar on the right.
The door in front of you should now start opening as the guard behind it comes through. Run at him shooting, heading through the door. Go up the stairs on the left, there's a couple of guards here, just dodge straight past them. Round the corner and there's a guard straight ahead of you. Shoot him (so he doesn't shoot you in the back) and run up the corridor. Head straight to the bottom, you might have a soldier to shoot at the bottom of the corridor. Go into the room at the bottom left of the corridor.

Now, if Dr. Doak is here, there'll be three scientists in this room. If Dr. Doak is here, run up to him until he starts talking. If he isn't here, you will have another chance before quitting and starting again. This is detailed after this walkthrough under alternative ending.
Assuming he is, once he starts talking head out of the room, turn 180 degrees to you right and head up the corridor between the two rooms. Turn left at the bottom, and shoot the two guards, sprint to the door up on your right, select the decoder and open the door. Once it opens, head through the door into the bottling room.
Head down the stairs, ignore Trevalyn and blow the tanks. You do this by tossing mines high up above the tanks and blowing them in mid-air (B + trigger together). Do this between the first and second row, second and third row, and fourth and final row. After they've blown, head straight out the double doors at the end of the room. You should be well inside the target time.

Alternative ending

Now, if Dr. Doak wasn't in this room, here's how you can still do this level. Turn around, shut the door so you're blocked in the room and stand against the door. The door opens into the room so this'll stop the guards opening the door. Alternatively, you can stand back from the door and shoot guards as they come into the doorway.
Either way, you'll have to shoot all the soldiers that come your way. There's a big backlog, so expect a lot of shooting and a lot of slowdown. Once their all dead, head out the door, turn 180 degrees and head into the big room on your left. Dr. Doak may be here amongst the scientists, if he is, go up to him to get him talking then head out of the room, turn left, go down the corridor, round the bend and open the door on the right using the decoder. There won't be two guards to shoot this way. If there is no Dr. Doak then you'll need to restart.
Once through the door, you can complete the level as above. Having to shoot all the soldiers will take a chunk out of your time, but you can still do it within the target time (it'll be tight though - this is the method used to get the achieved time listed for this walkthrough).