Written by my friend
Rave Monkey87 i am posting it becase it wouldnt let him
The prisoner who you need to rescue is in a ditch with tents near the beginning of the mission, right after the first locked fence. Before going to the fence, take out the guard in the guard tower who is shining a spotlight, by going to the right of it and up some rocks. Shoot him with your silent pistol and proceed crouched to the locked fence. Wait for a jeep and a truck to both pass to your left. The two guards by the fence will separate. When the truck disappears off of your map (if you identified it with your binoculars) open the fence. Push through gently and proceed to the left to a red and white barrel. There will be a guard around the corner to the right. Put him to sleep. Pick up his body and put it in the booth diagonally to the left. Climb the guard tower next to it and wait for the guard up there to finish speaking on the walkie then melee him (R trigger). Take over the spotlight and aim it to the left by the outhouses and you can see the prisoner who you need to rescue. At this point, if u have done everything I have written you should be able to pick up the prisoner (hold B button) and re-trace your steps back to the beginning cliff you started at. Call in your helicopter right away to said cliff (start button, menu index, third option down, SW landing zone on the map) as it takes a minute or so to arrive. Put the prisoner on the chopper (Hold B) and the achievement should unlock.
Sorry for the long solution, but it's my first time writing a solution for TA and I felt it would be better to explain everything than to be vague and have several questions asked. Good luck and happy hunting...