When a commercial flight from Germany lands at Boston's Logan Airport without a single passenger or crew member on board alive, FBI agent Olivia Dunham is assigned to the investigative team. When her partner and lover John Scott suffers severe chemical burns, she seeks help from Dr. Walter Bishop a one-time university professor who experimented in the same field but has now been institutionalized for 17 years. To get his cooperation however, she has to get Bishop's son Peter's cooperation as well. The information they gather leads to Massive Dynamic, a huge ...
An employee of Massive Dynamic covered in mysterious cuts jumps out a window believing himself to be attacked by a swarm of butterflies. Meanwhile, Olivia becomes fed up with her visions of John Scott and decides to go back into the sensory deprivation tank to get rid of them.
After a series of mysterious bank robberies, a suspect is found embedded into a wall, causing Walter to realize that they have not only found a way to literally walk through walls, but are looking for something he's made in the past.
When a second victim is discovered with injuries to the back of the neck, Fringe division is called in to investigate. Walter does an autopsy and discovers that the injury was inflicted by a human bite; the wound is infected by a rare genetically modified syphilis virus and all the spinal fluid has been drained. Tracing users of the virus leads the team to a scientist with connections to ZFT. His story leads the team to find more victims and a desperate race against time to track down a killer with a dangerous addiction to human spinal fluid.
When a woman bursts into flames and explodes, Olivia and Peter start to look into it, and Olivia starts seeing things -- which Walter explains as possibly her seeing an alternate reality. The investigation leads back to the experiment Olivia was part of as a child, and points to a high member of the FBI as well as links to Massive Dynamic. Meanwhile Nina comes to Broyles with her concern that The Observer has been sighted again, and frequently.