: Throughout the episode, Walter is haunted by "hallucinations" of a mysterious man—revealed to be Peter Bishop trying to break back into the timeline.
: Walter realizes the fungus is a vast neural network functioning like a giant brain. It protects Aaron by attacking anyone who threatens him, but the bond is symbiotic; killing the fungus could kill Aaron. [S4E3] Alone in the World
The Fringe team investigates the rapid decomposition of two 12-year-old bullies found in a tunnel. Their investigation leads them to Aaron Sneddon, a lonely, artistic boy who has forged a psychic bond with a massive, parasitic fungal organism Walter names "Gus". Key developments include: : Throughout the episode, Walter is haunted by