Fringe Season 2 Episode 10: Grey Matters

As the show opened last week, a mental patient was undergoing brain surgery by someone from the other side. While undergoing the surgery, he is discovered and leaves the man with his brain exposed.

The Fringe team comes in and learns that before this apparent surgery, the patient was crazy, but has become completely sane since having his brain opened up. After doing some research, the team finds out that this has happened several times to different patients at different mental facilities, including Walter.