After completing all three chapters, you'll find a safe key in the bathroom sink where you picked up Lucy's jaw after finishing chapter 1. Leave the bathroom and turn left twice and open the door to the study room. The safe is on your left. Inside you'll find a note.
Head to the basement and go down the hallway behind the couch (opposite the TV, where you found the camera during Lucy's chapter). You'll see room 302 at the end of the hall, open up the door and you'll earn this achievement (and get a nice little spook).