Masks Off is the 17th mission of Crysis 2. For this walkthrough, players will extract Hagreave (the man helping you over the radio all this time), and then escape the Prism facility, as it is under siege by the aliens. The mission is significant for providing a lot of new interesting answers and backstory to the main plot of the game.

1. After the cutscene, Follow the woman into the elevator.
2. You will need to get past (or clear out) Hagreave's guards in order to extract him.
3. Try to take a stealthy approach as alerting the enemies of your presence will get them all to converge on you.
4. A good place to start is to go down the hallway to the right instead of taking the main hall with all the guards.
5. Stealth kill the lone guard in the room and proceed on. As you did just now, try to take the route with the least guards.
6. Note: keep in mind to constnatly resupply here. Ammo caches are abound as usual.
7. Make your way up the stairs to the left.
8. Jump behind the guard coming straight at you from the stairs. Either stealth kill him, or move past.
9. Continue on to the third floor.
10. Navigate through the soldiers. Since there are a lot of hallways on this level, it should be easy to dodge them in stealth, unless of course you choose to kill everyone!
11. Open the objective doors and head inside.
12. Approach the wall under the computer screen. It will open, revealing a room with a body in some kind of protective status. Wait for a mission update.
13. Take the syringe on the desk behind you.
14. Use it.
15. After the cutscene, aliens will drop down into the room. You won't be able to fire, and will have to escape by running to the door you will see opening on your left. Run quickly or you will die!
16. Make your way out of the facility. Use armor mode when you're in the electricity area.
17. Take any supplies in the room with the closed door.
18. Open the door.
19. As Hagreave just said, the CELL soldiers will now help you, so don't worry about them.
20. Head to the objective point. Keep in mind that since you don't have to defend anything, you don't necessarily have to kill the aliens to get past them.
21. Follow the road around the left, and then go into the opening on the right.
22. Go up the stairs and continue on to the objective.
23. Here, you won't have much choice but to kill the aliens first. Use the attached machine gun near you if desired.
24. Clear out the aliens defending the building and head inside. Keep in mind there's a Tank down below, and some aliens will also jump in from the sides and behind you.
25. Go up the stairs go into the hallway on the left.
26. Break and jump through the glass on the right.
27. Continue towards the objective.
28. You can ignore most of the enemies here, and run straight for the partially-open gates at the South end.
29. Enter the elevator and go up.
30. Run across and use the next elevator.
31. Continue down the road to the objective. Kill the aliens.
32. Continue making your way down the bridge. 
33. When the way is blocked, you will have to jump up to get to the area above.
34. In this area, you can just run through as you did before.
35. Press F to grab as instructed, when the cutscene begins.