Season 4, Episode 3:
Alone in the World
Fringe Division investigates a strange fungus after it starts killing people, and Walter comes to believe that it's symbiotically linked to a young boy who survived the first known encounter with it.
Meanwhile, after a psychological examination, Walter tries to demonstrate that he's functionally sane to avoid being sent back to St. Claires — a task that's made all the more difficult by his hallucinations, which are getting worse. At the end of the episode, he attempts to give himself a lobotomy to try and stop the visions, but Olivia stops him at the last moment. He explains his hallucinations and Olivia reveals that she's been seeing the same man (Peter) in her dreams, and that she drew an accurate sketch and has been trying to identify him using the FBI databases, with no luck. After learning this, Walter becomes convinced that the man is real and they have to find him.
- Alien Kudzu
- Body Horror: The bodies infected and devoured by the fungus.
- Eye Scream: Walter attempts to lobotomise himself in an attempt to get rid of his hallucinations. Luckily Olivia stops him but not before we get a shot of the pick inserted into his eye.
- Festering Fungus: The fungus, dubbed "Gus" by Walter.
- Walter also mentions the cordyceps.
- Freudian Slip: "You're going to kill Peter!"
- Guardian Entity: The fungus acts as one for Aaron.
- Kill It with Fire: Walter first suggests UV Light, but Olivia immediately suggests flamethrowers.
- Psychic Link: The fungus formed one with Aaron. As a result, the Fringe Division can't kill "Gus" without possibly killing Aaron. Walter then has to talk Aaron into severing that bond emotionally.
