Season synopsis
Contains spoilers for this season and earlier seasons.
In 2036, the Observers have conquered Earth and impose control through loyalist collaborators. Olivia, Peter, their adult daughter Etta and Walter reunite after Walter is freed from amber, then recover his recorded instructions for a plan to defeat the occupiers. The team searches for components and allies while evading Captain Windmark. Windmark kills Etta after the team retrieves an equation needed for Walter’s plan, and Peter’s grief drives him toward revenge. He implants Observer technology in his brain to predict Windmark’s actions, but the change makes him increasingly detached and violent; Olivia eventually persuades him to remove it.
The recovered tapes lead the group to Donald, who is revealed to be September after being made human by the other Observers. He explains that Michael, the quiet child Observer recovered during the search, is genetically unusual: he has emotions while retaining advanced intelligence. In 2167, a scientist will start eliminating emotion to increase intelligence, producing the Observers who later invaded Earth. The plan is to send Michael to that moment so the scientists reconsider their choice. September says he will take Michael, but he is killed before the plan can be completed, leaving Walter to assume the sacrifice.
The resistance assembles the apparatus and carries out the plan while Windmark attacks. Olivia draws on the Cortexiphan treatments to kill Windmark, and the team gets Michael through the time portal. Walter travels with him to 2167, where Michael can influence the scientists. The invasion is prevented and the timeline resets to the day the Observers first arrived in 2015. In the closing scene, Peter and Olivia are again with young Etta, while Walter is absent because he went to the future with Michael. Peter receives Walter’s envelope containing a drawing of a white tulip, the farewell prepared before the operation.