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 watcher has been sighted again, and frequently.
A highway construction worker in rural Pennsylvania goes missing when he is mysteriously drawn into an underground tunnel filled with human remains. Meanwhile, back in the lab, Walter is attempting to simulate travel between realities on frogs. When it's discovered that the disappearance in Pennsylvania is not an isolated incident, the Fringe team travels to the crime scene to dig up evidence.
Peter, Walter, Olivia and Broyles pursue a strange and deadly occurrence in Philadelphia where a bomb blew up inside a train station but left no trace of any explosive device. The perplexing and unexplained set of circumstances returns Walter to the lab to closely examine the human remains where he uncovers an unlikely energy source that triggered the explosion. With the explosive threat of more bombs and links to a classified military project, the intense investigation leads Olivia and Peter to Iraq.
Recuperating from the traumatic and alarming meeting with Massive Dynamic founder William Bell, Agent Dunham consumes a powerful "fringe" concoction that Dr. Bishop prescribes to stimulate her memory. Meanwhile, the Fringe Division investigates a series of robbery cases that are tied to shape-shifting. As clues are tracked and memories are jogged, another woman experimented on by Dr. Bishop is introduced and a flashback reveals more about Olivia's visit to the alternate reality.
The Fringe team travels cross-country to Seattle after learning of a mysterious incident involving a man who attacked his boss because he believed he was an evil ram-horned creature. As these puzzling occurrences continue, the team tirelessly explores strange and creepy links to dreams. In pursuit of additional information, Agent Broyles has a disconcerting meeting with enigmatic Massive Dynamic executive Nina Sharp that leads the investigation in an unthinkable direction.
Strange deaths by a mysterious shadow leads the Fringe Team to the scene where they learn that a Russian astronaut was possessed by an alien and his brother is convincing Dr. Bishop to solve the equation to free him.
When a kidnapping rapidly escalates into a hostage situation in New York, local authorities close in on the suspects only to discover a mysterious force with mind-blowing consequences. As the investigation intensifies, the mystery and threat deepen to unimaginable proportions when the Fringe Division connects a link between the kidnapping and Massive Dynamic.
When a peculiar abduction occurs in Boston, the Fringe team uncovers details of the mysterious man known as The Observer. While the bizarre case takes center stage, Walter, Peter and Astrid hit the lab to analyze unusual evidence and deal with Walter's insatiable appetite for a milkshake.
After a cargo ship runs aground, the shoreline becomes littered with bodies hosting a giant squid-like creature. The Fringe team descends upon the scene to examine the bodies and discovers that the mysterious organisms are actually giant parasites. As the investigation unfolds, Walter heads back to the lab while Olivia, Peter and Broyles race against time when they realize the case has ties to a threatening organization.
A Fringe investigation is triggered when a patient at a mental institution undergoes an impromptu brain surgery that unexpectedly leaves his brain exposed. Despite the unthinkable circumstances, the patient's condition and sanity miraculously improves before the Fringe team arrives. While Agent Dunham and Peter scan surveillance tapes (and Walter enjoys his pudding), Olivia recognizes a familiar face as Thomas Jerome Newton, the leader of the "shape-shifters." As similar cases stack up, the Fringe team heads back to the lab to determine exactly how patients are being ...