Through the Looking Glass and What Walter Found There
Walter discovers that one of his tapes holds the key to defeating the Observers. To obtain it, he must travel to an abandoned apartment building where time and space are compressed. Peter, Olivia, and Astrid follow, and Peter discovers that he may be able to fight the Observers directly.
Fringe follows the casework of the Fringe Division, a Joint Federal Task Force supported primarily by the Federal Bureau of Investigation, which includes Agent Olivia Dunham; Dr. Walter Bishop, the archetypal mad scientist; and Peter Bishop, Walter's estranged son and jack-of-all-trades. They are supported by Phillip Broyles, the force's director, and Agent Astrid Farnsworth, who assists Walter in laboratory research.
The Fringe Division investigates cases relating to fringe science, ranging from transhumanist experiments gone wrong to the prospect of a destructive technological singularity to a possible collision of two parallel universes. The Fringe Division's work often intersects with advanced biotechnology developed by a company called Massive Dynamic, founded by Walter's former partner, Dr. William Bell and run by their common friend, Nina Sharp. The team is also watched silently by a group of bald, pale men who are called "Observers".
Fringe - Through the Looking Glass and What Walter Found There Synopsis and Schedule