Fringe: Season 3, Episode 8

3 - 8: Entrada

Realising she has been exposed, Fauxlivia drugs Peter and escapes. The next morning, the team find the typewriter (a "quantum entanglement" device) used to contact the parallel universe in a typewriter store in the Bronx. Peter discovers the location where Fauxlivia is going to return to her universe. The team arrive at the station to find Fauxlivia holding a hostage, which is revealed to be a shapeshifter who earlier injected her with resonating rods; Peter kills the shapeshifter and Fauxlivia is arrested. Meanwhile in the parallel universe, doctors prepare to kill Olivia and use her to help Fauxlivia return (it would require a body with the same mass as Olivia to achieve it). Broyles manages to break her out. Olivia finds Walternate's tank empty, so the two go to Walternate's old lab in Harvard. She lies in the isolation in time before Broyles is arrested. Olivia successfully crosses over back to the Prime universe, while Fauxlivia returns to hers, leaving behind the mutilated body of "Alternate-Broyles" to make up for her mass. While Peter and Olivia reunite at a hospital, the typewriter store owner trades a man a piece of the doomsday device in exchange for the restoration of his paralyzed legs.