Who are you? After sacrificing himself to save both worlds, Peter mysteriously returns to ours. But he has been forgotten by Olivia, by Walter, by everyone. It s as if he never existed. At the same time, shapeshifters controlled by an unknown master begin an onslaught of destruction, and now the two former enemy universes must cooperate to defy a common foe. Fringe s thrilling 22-episode fourth season continues the inspired series synthesis of astounding phenomena, baffling secrets and dramatic, character-driven stories. And in this season, events may prove that the most powerful force in our universe or theirs is not a doomsday device, not a paranormal force, but human love.