Complete story — includes the ending
David Robert Jones holds Olivia and Nina captive, torturing Nina to activate Olivia's Cortexiphan-induced abilities. Olivia recognizes from Nina's answers to questions about their shared past that this Nina is in fact the one from the parallel universe. However, Olivia plays along, explaining to Nina that her abilities could only be activated by being near Peter. The Observer September appears in the lab, bleeding from a chest wound. With Walter's help, Peter enters the Observer's mind to learn of Olivia's location. He finds out that the Observers are scientists from one possible future of humanity. When September tried to observe the point where Peter's cure was discovered, he caused several unintended changes within the timeline, including the war between the two universes. September explains that Peter's reappearance may be a means to set things right, and insists he find a way to reunite with his original Olivia. Finally, September tells Peter to "go home". Peter wakes up in the lab, and September's body vanishes. Following September's advice, Peter returns to his home, from where he is abducted by Jones' men. He is brought to the same facility as Olivia and tied up. Olivia uses her powers to free herself and Peter, but Jones and Nina are able to escape. Peter tells Olivia that he fears he has been unintentionally imprinting his memories of "his" original Olivia onto her. Consequently, he leaves her.
Sources and content license
Source and revision history · Adapted from Wikipedia contributors, Fringe season 4. HTML formatting and reference markers removed. · Content license