Stiles went missing for 3 years. When he came back, he never talked about what happened. The FBI separated everyone, so he can't talk to anyone from the time he was gone. Scott saw how reserved he was and how much he truly changed. He went to Deaton to see if he could help. Deaton knew of a way but knew Stiles wouldn't like it. Deaton contacted a friend of his and told them the problem. They knew what to do. When everyone least expected it, they were surrounded by white before being placed into a room that looked like a movie theater. They learned that they were going to watch Stiles' memories. Like predicted he didn't like it, in fact, he hated it. But they soon realized they weren't the only people in the room. The survivors were there.