It's November 2036, in some bleak universe where the Observers rule.
They seized control in 2015. The original Fringe team fought them but lost. Humans who survived "the Purge" were labeled "Natives," and some factions, called "Loyalists," pledged allegiance to the Observers. Fringe Division continued, but only to police the Natives. Resistance was quickly overcome . . . or so the Observers thought.
In Boston, young Fringe agent Etta retrieves Native club owner Rick from a confrontation with the Observer boss, Captain Windmark. Natives are HER jurisdiction. Windmark looks searchingly at Etta, remarking that she is always exactly what she seems. In the alley, Rick comments on Etta's unique ability to fool Observers when they read her. He shows her something inside a van. She grasps her necklace when he says there were two more, a man and a woman. But he couldn't move them all out of the City together. Suddenly, he's killed by a Loyalist assassin. Etta escapes in the van. The cargo? Dr. Walter Bishop, in amber.
At Fringe HQ, Etta tells her boss, Simon Foster, she had an old order with Rick, for information on the missing team. Simon scoffs that the original Fringe team didn't mythically disappear; they died 20 years ago. She shows him Walter, stashed in a lab.
Meanwhile, Captain Windmark tells Agent Phillip Broyles - who's older, careworn, but as flinty as ever - to solve this recent spate of Native-on-Native killings. Or else.
Walter's trapped in third-generation amber, which can only be reverted to a gas momentarily. He won't become conscious quickly enough to escape before it re-encases him, and if they push him out, they'll be trapped themselves. Simon cleverly uses a wand that delivers a concussive blast - an early Observer crowd-control device - to knock Walter clear just when the amber becomes gaseous.
Walter's so hungry. Do they have anything to eat?
Simon gives Walter red licorice, which the stories say is his favorite. Etta shows him a holographic blueprint of a device he was reportedly working on, to get rid of the Observers. Unfortunately, Walter's no longer merely eccentric. He has serious neural damage.
Etta visits a white-haired Nina Sharp, who uses a futuristic wheelchair, at Brooklyn's Ministry of Science. Though seemingly hostile toward Etta, Nina's on her side. And she's astonished to see Walter, who doesn't know her.
Nina explains they can use a piece of Walter's brain locked up at Massive Dynamic to inspire his brain to heal. However, it's at the old facility in the City - which is wall-to-wall Observers. While waiting for Simon and Etta to arrange transit passes, Walter fixes Nina's robotic arm.
At the monorail station, Walter shouts "Monster!" at an Observer. The trio tell a questioning Loyalist officer they're taking Etta's crazy grandfather to visit her grandmother's grave.
At Massive Dynamic, they unknowingly trip an alarm. A Fringe agent informs Broyles, who calls Windmark. Simon and Etta inject the neural material into Walter's brain. He passes out, and they wait.
Simon says the Purge happened during his freshman year at Stanford. They watched on TV as Observers killed people in the streets. He suddenly knew his parents sent him so far away to protect him, because they were in the Resistance. They died, and he vowed to never give up. Etta was only four when she last saw her parents. She touches her necklace.Walter awakens. He's brusquer, sharper. Meanwhile, an Observer and Loyalist troops search Massive Dynamic.
Walter examines the holographic plans. He recalls how September tried to help them. What happened to him was, well, unexpected. He told Walter that, by 2609 AD, they had thoroughly poisoned the planet. So they traveled back through time and took our planet. His mood hardens. He'll build the device. Etta asks if he remembers where his team is. He looks at her sharply and says, "You?"
The troops arrive. Walter touches a place on the wall, which magically slides back. He says neither he nor William Bell ever left themselves only one way out of a room. In another lab, he wires a small cylinder, saying resistance must take place at any opportunity. We are insurgents, and this - he places the cylinder into a larger container - is antimatter. They escape. The pursuing Observer just realizes what's happening, when WHOOOM! Massive Dynamic implodes.
Broyles takes a report from the Loyalist who detained the trio earlier. He has an agent activate Foster's tracker and assemble a team.Walter's team is ambered in a large basement. Simon gets Astrid out, but breaks the wand. As he and Etta work on it, Astrid goes to an ambered area the agents can't see - containing William Bell. Walter appears and says, shh. Then he points a small device at the amber.
As sirens approach, Walter says we need him out of there, now!
Shortly later, Broyles finds Simon ambered, frozen in the act of pushing someone away. Nearby is a piece of red licorice.
On the monorail leaving the City, Astrid can't believe Walter left Bell behind. He says remember what he did to Olivia; even you can't be that compassionate. But, protests Astrid, how will we get access - Walter interrupts, indicating his bag, which holds Bell's hand, still ambered. They have everything they need.
Etta fiddles with her necklace, which is half a coin. Peter approaches, and she emotionally says, "Do you know me?" Puzzled, he says he's been in that amber for over 20 years, and she barely looks old enough to -
Realization dawns. Peter says, "Henrietta?" She smiles and says, "Hi, Dad." They embrace.