Push It

First Floor - The Middle Obstacle: You'll start on the first floor, and the biggest headache is that group of guys chilling in the middle. Your first move is to take out the dog and the sentry in the west room. Once they're down, grab a gun. Blast the first guy you see in the center room. Don't stick around though – immediately run back and hide in that west room. The other guys will come looking for you. Just pick them off as they come. Keep repeating this until the middle room is completely clear. After that, just sweep through the remaining rooms, one by one, to finish up the first floor.

Second Floor - South-West Section: Head up to the second floor and make your way to the south-west part. This area is much easier if you stick to melee. Grab a melee weapon and take it room by room. The key here is to avoid making noise. When you enter a room, try throwing your melee weapon or slamming the door shut right as you enter. This can often take out an enemy before they even know you're there. I found moving counter-clockwise around this section worked best.

First Floor Again & South-East Stairs: Now, head back down to the first floor and find the south-east stairs. Go up them.

Second Floor - South-East Section: You'll encounter a smoker sentry pretty quickly. Lure him closer and take him out. Then, make a dash for the guy in the north-west corner. As soon as you've dealt with him, duck into that north-west corner and wait. More enemies will come to investigate. Take them out as they arrive. After clearing that group, move on to the guys in the east room. The last few enemies in the south-west area of this floor shouldn't give you too much trouble.

PUZZLE PIECE: Keep an eye out on the second floor, specifically the south-east stage. On the big dance floor there, you'll find the letter "R" in the north-east corner. Grab it!

All Done: Once you've got the "R", head back to the car to finish the mission.