Letters In Transit
Fringe Season 4 Episode 19 (04/20/12)
In the year 2015 the Observers stopped observing and took over. Despite their best attempts, people were defeated and Observers ruled.
Fringe agents, while allowed to operate on behalf of the natives, had never given up the fight and we joined Simon and Etta as they discovered Walter and his team in amber. Until they were discovered, Nina and Broyles were the only members of the original team left in the fight and they had aged significantly.
After suffering brain damage due to his amber release, Walter's previously removed brain tissue was utilized to restore his health. He lead Etta and Simon to the rest of his team and he set free Astrid and Peter. William Bell was with them, but apparently he killed Olivia, and Walter chopped off his hand and left him in amber rather than free him.
Etta had an odd attraction to the team, and it was revealed she was the child of Olivia and Peter.