F.E.A.R. Files

Simple, like it says, just get to this point in the campaign. The difficulty doesn't matter. The achievement just pop after the screen fades out at the end of the mission "The Plaza Chase"

This is the third of six "progress" achievements. You are about halfway through the game

Here is a great walkthrough if you get stuck:
http://www.gamefaqs.com/computer/doswin/file/941968/51786