Fringe/Recap/S04 E01

Season 4, Episode 1:

Neither Here Nor There
After the events of "The Day We Died", the Fringe Divisions of both universes are reluctantly resolved to work together, whilst still dealing with the Fringe cases of their respective worlds -- neither side realising that Peter Bishop has been erased from time. In the prime universe, Olivia and Astrid investigate, with Walter observing from the lab via remote cameras, when an FBI agent is killed by a transulscent man. The victim's parter is Agent Lincoln Lee, who has never met the Fringe team in this timeline but still insists on being part of the investigation. He is eventually transferred full-time to Fringe Division after helping Olivia to stop the multiple transluscent killers. When Walter performs an autopsy, he discovers that the killers are new forms of the shapeshifters, so Olivia and Lincoln meet Fauxlivia in the DMZ -- the bridge between the two universes, created by the Machine -- and pass the information on so that the alternate universe's Fringe Division can investigate.

Meanwhile, Walter -- now a complete shut-in who lives in the lab and hasn't left since being released from St. Claire's -- starts to think he's going completely insane after seeing visions and hearing voices in the lab. At the end of the episode, he breaks his TV after seeing someone reflected in the screen, someone he doesn't recognise but the audience does: Peter.