When the sheriff of a small town nearby Edina City gives a ride to a boy that is fleeing home, he finds at the police station that the boy has changed to a deformed child. Out of the blue, a group of deformed man slaughter the sheriff and two marshals and bring the boy with them. The Fringe Division is assigned to investigate the case and they head to Edina, here they are received by the local sheriff. They overhear a humming and the sheriff explains that it comes from a military base. Soon Olivia and Peter are attacked by a local in a truck but Peter succeeds to kill him. They bring the corpse to Dr. Bishop that catches a rare butterfly to Astrid that collects the insect. But when he deliver the pot with the butterfly to her, she has turned into a moth. Astrid and Dr. Bishop drive to Edina City and when the moth becomes a butterfly again, Dr. Bishop discovers the secret of Alina City.

After a man spreads a pathogen on the grounds of a company, the Fringe team start an investigation. While stuck inside the quarantine zone, Peter and Olivia try to identify the origin of the pathogen. Outside, Walter tries to find a cure.