1. Head down the stairs and turn right.

2. Wait for this technician to enter the room. Drag him to the dark corner (inset) and knock him out.

3. Take out this technician. Hide the body with the other.

4. Use this red terminal to complete the objective. You are given the door override code for the weapons testing department - 110700.

5. Backtrack up the stairs and through the Static Dispersion Chamber. Shadow this guard to pass unnoticed down the hall.

6. The ladies' room on the left has a medical kit.

7. You can't pass undetected through the metal detectors, so use your sticky shocker on this guard. Climb through the window and take the guard's satchel for a medical kit.

8. Continue to this lobby area. Your immediate goal is indicated by the arrow. Time your approach to avoid the two security cameras.

9. Dash down the corridor to this hiding spot.

10. Pass by the window when the employee's back is turned. Take the stairway on the left.

11. You can safely enter the door override code for the weapons testing department from here - 110700.

12. Wait here until this employee finishes his phone call. Knock him out when he goes to the soda machine. Hide the body in a dark area.

13. Continue through the corner door. Use the computer to learn about the turret. Note the flare on the ground near the turret, and the flares to the left of the computer.

14. Select a flare from your quick inventory, light it and toss it in front of the turret. The turret will take aim and fire. Lesson: you can then interact with the turret control chest while the gun is turned away.

15. Pick the lock on the door behind the turret then take the elevator up. Exit the elevator to load the next area.

16. Enter the Media Room.

17. Sneak behind the white board and the desks to the door around the corner.

18. Don't miss the view of Virginia's October countryside.

19. Dougherty's office is 508.

20. Use Dougherty's computer to complete the objective.

21. Exit Dougherty's office to the right and head down this corridor.

22. Enter the auditorium on the left.

23. A briefing is in session so move quietly. Cross through the main aisle as indicated.

24. Play with the projector light - it's gorgeous.

25. Wait for this guard to walk to the projector room, then pick the lock on this door.

26. Exit the auditorium and turn left.

27. That's Dougherty at the end of the corridor heading for a smoke. Sneak past this break room on the right. There are bathrooms on the left with nothing to offer. Enter room 501 on the right.

28. Inside are two employees. Grab the standing one and knock him out in the hall.

29. Finish off the second employee. Access the computer to learn the Information Retrieval Service Door code - 0614. Return the other body from the hall - for now.

30. The keypad is just across the hall. Enter the code 0614 and pass through the double doors.

31. To the left you'll find this UFO Sightings Office. Pick the lock and enter.

32. Use the computer inside to read an encrypted email - with the recurring number 020781.

33. Enter the code 020781 on this keypad.

34. Row upon row of X-Files. On the table to the right are two sticky shockers. On the table to the left are three sticky cameras. Hide the bodies from office 501 in this corner (inset). Backtrack to the hallway.

35. The smoking area - and Dougherty.

36. Wait for the guard outside to pass before grabbing Dougherty.

37. Head for the indicated area, careful to time your maneuver to avoid the guard.

38. Continue along the catwalk.

39. Lambert updates your objectives on the way down these stairs.

40. Dougherty must be temporarily set down to open this door.

41. Descend the stairs and hide his body under the stairwell.

42. Your heat vision makes it easier to keep an eye on the guard and the maintenance technician in the next area. Knock out the technician in this dark area.

43. Use a sticky shocker to take out the guard.

44. Exit through this door. Note the sticky shocker on the right.

45. Take out this guard with a sticky shocker.

46. Climb down to the roof then drop to the ground below.

47. Grab the guard from behind and knock him out.

48. Go up this ladder and return to Dougherty's body.

49. Retrieve Dougherty from beneath the stairs.

50. You can't climb down the roof with Dougherty's body in tow. Around the right of the building are stairs - blocked by this guard. Put down Dougherty's body for the time being and use a sticky shocker to take out the guard.

51. Pick up Dougherty once again and take him down the stairs.

52. Drop dougherty at the van to complete the mission.