Listen to Hartman's recordings.

At the beginning of episode 4 you'll be in Hartman's lodge, when night falls and Alan manages to get his hands on a key, you'll be able to access the staff wing. After unlocking the door and opposite the picture of Hartman, there is a small conference room full of paintings, with a manuscript page in. Straight ahead of you as you walk in there is a tape recorder. Listen to the three recordings to get your achievement.