Lab Rat is the fifth mission of Crysis 2. For this walkthrough, players will navigate Dr. Gould's lab, in order to locate and destroy his computer data, and meet up with Gould afterwards. As the lab is crawling with CELL soldiers, the player will have to employ a sneaky playstyle to carefully navigate through large numbers of enemies packed in a relatively small area. The mission is also significant for having the first "boss" fight of the game, against a Gunship.

1. Put your cloak mode on, and drop down through the window
2. Carefully stealth kill the soldier in front of you.
3. Note: this soldier's weapon is very good for this level, if you choose to snipe the soldiers from this roof instead of employing a more stealthy approach.
4. If you choose the sniping approach, make sure to use nanovision, as it is difficult to spot all the enemies below you. Also, make use of explosive barrels (marked with a weak blue light in nanovision) by shooting at them when enemy soldiers are nearby.
5. Another effective strategy for getting through here is to take the left roadway, around the majority of the soldiers.
6. Make your way under the half-open garage door towards the objective.
7. To start off, stealth your way to the room just down the hall and take the ammo/grenades.
8. Clear out the enemies by the elevator doors. Watch out for the soldier manning the mini-gun.
9. Go inside the elevator. It will go up automatically.
10. Take out the 3 soldiers quickly as suggested by Gould.
11. Shoot the computer terminal (its located right under the blue objective marker) until you get the mission update.
12. When the CELL helicopter appears, quickly zoom in and snipe out the gunner. Make sure to be near cover so that you can avoid enemy fire while aiming. The best position here is to peek over a wall in the smaller room, and shoot through the windows on the left.
13. Note: Armor mode is very useful for this as the gunner will take a quite a few hits to kill, and will still fire at you.
14. While still in the smaller room, aim at the elevator from as far away as possible. You will be able to easily headshot the 2 soldiers coming up.
15. The helicopter will now return with a new gunner. Once again, zoom in and take him out.
16. Look up at the glass roof above you. There will be 2-3 soldiers throwing down grenades. Snipe them out.
17. Continue killing soldiers while you wait for the Gunship to return.
18. Now you can start actually shooting the Gunship itself. Aim straight at it with Armor mode on, and shoot while near cover. Hide behind the wall to reload. It should only take about 3 full clips with a SCAR/SCARAB Assault Rifle.
19. Go through the hole in the wall created by the Gunship crash and make your way left, across the water over the yellow metal tower. As usual, you can decide to completely ignore enemies, kill everything, or any other style you prefer.
20. A stealth approach is definitely favoured here though. You can take out the guard at the bottom of the stairs, and then stealth past the others.
21. Power kick the objective door to get in and continue on.
22. Wait for Gould to send the elevator down when you reach the objective, and get in it.
23. Follow Gould into the apartment, and walk up to the nano chair.
24. Follow Gould into the other room.
25. When the soldiers start shooting, you won't be able to shoot back for a while. Just follow Gould out out of the room.
26. When you find yourself in the hallway again, wait for the soldiers to bust in through the door down the hall. Kill them and head through the open door towards the objective, killing more soldiers on the way.
27. You will automatically initiate a cutscene when you reach the objective, ending the mission.