Olivia returns from the alternate reality and Peter tries to get information about her visit. Meanwhile, Walter makes some custard for his son's birthday, and Broyles deals with the threat of a government shutdown of the Fringe Division. 

A Pennsylvania highway construction worker in rural Pennsylvania is mysteriously drawn into an underground tunnel filled with human remains. When it appears that the disappearance is not an isolated incident, the team travel attend the scene to search for evidence. Meanwhile, Walter attempts to simulate travel between realities on frogs. 

When a train station is bombed, it's a race against time to investigate for Peter, Walter, and Olivia. Walter soon discovers something mysterious about the human remains. 

Dunham is still recovering from her traumatic visit to the alternate reality, and Walter gives her a concoction to aid her memory of the happening. Meanwhile, the team investigate a series of robberies that are linked to shapeshifting. 

In Seattle the team investigates a man's attack on his boss, who he thought was a ram-horned demon; Broyles has a disconcerting meeting with Nina Sharp of Massive Dynamic. 

The Fringe Division undertakes a puzzling investigation into why victims are disintegrating into ash; the case casts light on Broyles' past; personal details about the division leader emerge. 

A kidnapping rapidly escalates into a hostage situation, and authorities closing in discover that an unknown force has mind-blowing consequences; Fringe Division identifies a link between the incident and Massive Dynamic. 

A peculiar abduction in Boston leads the team to uncover details of the mysterious man known as the Observer; Walter, Peter and Astrid analyze unusual evidence and deal with Walter's insatiable appetite for milkshakes. 

Olivia and co investigate when a cargo ship runs aground, littering the shoreline with bodies. After following the clues, they make a disconcerting discovery. 

The brain of a patient at a mental hospital becomes unexpectedly exposed after undergoing an impromptu surgery. William Bell returns, while Olivia encounters a familiar face 

After a teenage girl is pronounced brain dead she mysteriously reawakens, seemingly with the mind of a high-ranking Russian soldier 

Following an unexplained attack involving disfigured humans, the Fringe team visits Edina City, a small town in upstate New York to uncover leads surrounding the bizarre case. 

A painful explosion of blood coincides with the death of a Dutch industrial consultant. Olivia and Peter fear that others will be contaminated after discovering that the blood contains pathogen. 

Unseen killers target a wedding with a toxin that targets specific individuals, and Walter discovers that the case may be tied to a branch on the Bishop family tree. 

After a violent tremor shakes a Manhattan office building to its core, the Fringe Team believe the only survivor is not from this reality. Walter surmises that what shook the building was not geologic, but rather something discovered by him and William Bell many years ago. With another catastrophe imminent, the team races to Jacksonville. 

More morsels of Fringe's overarching mythology are unveiled when Walter flashes back to 1985 to explain Peter's other-worldly origins. 

When a perfectly healthy woman is found dead from a disease she never had, the Fringe team investigate the origin of this inexplicably fatal condition before it claims more innocent victims. 

The team investigate after all passengers aboard a commuter train appear to have died a still death. Bizzarely, all cell phones, mp3 players, laptops, batteries and bodies have been drained of power. A suspect by the name of Alistair Peck immerges, a very powerful man in possession of tremendous energy with severe consequences. 

The murder of two teenagers by shapeshifters puts the team on the trail of Newton and his people, a trail that leads to Massive Dynamic. Meanwhile, Peter tells Olivia about his family. 

Walter tells Olivia's niece Ella a fairytale, that includes musical performances by Olivia and Agent Broyles. 

Peter teams up with Sheriff Mathis on a mysterious murder case; Walter faces the possibility of being sent back to St. Claire's; someone from the "other side" visits. 

William Bell, Walter and Olivia make the trip to the alternate Earth to stop the collision of the two worlds - and the extinction of one. 

Walter and Olivia are forced to make some personal sacrifices on a visit to the 'other side', in order to prevent the two universes colliding.