Fringe/Recap/S01 E19

Season 1, Episode 19:

The Road Not Taken
A woman spontaneously combusts in a New York City street and the Fringe team investigates. Olivia begins having visions in which there are two victims, other people are subtly different and the city is in a much worse state: Walter theorises that her cortexiphan abilities are allowing her to catch glimpses of the alternate universe. These visions allow Olivia to find the victim's twin sister, who is also a pyrokinetic and was part of the same cortexiphan experiments as Olivia, and to stop a ZFT mole from kidnapping her. Walter reveals to the rest of the team that based on the typewriter, either he or William Bell must be responsible for writing the ZFT manifesto. He spends much of the episode searching for an original copy of the document, one that still has the chapter on ethics that is missing from the current version, but just as he finds it, the Observer arrives to take Walter away. Nina Sharp meets with Broyles to discuss the Observer: after returning to her apartment building, she is shot by a masked gunman.