Fringe: 4.19 Letters of Transit
We open with a text crawl that explains that the Observers seized control of our world in 2015, quickly defeating the original Fringe team and all organized resistance before purging millions of humans who wouldn't follow them. Now, the Fringe division exists only to police "native" (human) crime, while the Observers are satisfied that all major resistance has been crushed. Flash forward to Boston, 2036.
Inside the former Massive Dynamic building, the trio [Etta, Simon and Walter] accidentally set off an alarm that notifies Fringe division of a break in. Unaware of what's happening, Broyles notifies his Observer boss, Captain Windmark (Michael Kopsa). Inside one of the abandoned labs, Simon gives Walter a sedative and a shot using his old brain matter to heal his mind.
When Walter wakes up, he is remarkably lucid and even harsh towards the agents. Downstairs, an Observer and his cadre of armed loyalist soldiers prepare to shoot the intruders on sight. Upstairs, Walter reminisces about the Observer known as September, who tried to help humanity before Walter admits that he can build a machine that will get rid of the Observers. As the Observer and his men close in on them, Walter assembles an impromptu anti-matter bomb and declares himself and the agents to be insurgents.
Shortly thereafter, the Observer and his men find the bomb moments before it goes off and completely destroys the building. Walter tells the agents that he now remembers where the rest of his team is. Back at Fringe headquarters, the guard from the train station alerts Broyles that Simon and Etta were transporting Walter without proper clearance. As Broyles assembles a team to find them, he activates a tracking device in Simon's body. At the hidden tunnel, the trio free Astrid Farnsworth (Jasika Nicole) from the amber, shortly before she and Walter see another person who was ambered beside them: William Bell (Leonard Nimoy)!
But the device Simon used to free Astrid and Walter begins malfunctioning as Broyles' team closes in on them. Realizing that they have only one option to save another person in the amber, Simon takes his place. Moments later, Broyles and his team find Simon trapped in amber while one of Walter's trademark licorice links has been left behind. On a train leaving the city, Astrid chides Walter for leaving William Bell behind, but he reminds her that Bell did something to Olivia Dunham (Anna Torv) that Walter considers unforgivable.
Walter also reveals that he severed Bell's hand for an unknown purpose.
Source: Crave Online