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 onslought 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.

Episodes:

1. Neither Here Nor There
2. One Night in October
3. Alone in the World
4. Subject 9
5. Novation
6. And Those We've Left Behind
7. Wallflower
8. Back to Where You've Never Been
9. Enemy of My Enemy
10. Forced Perspective
11. Making Angels
12. Welcome to Westfield
13. A Better Human Being
14. The End of All Things
15. A Short Story About Love
16. Nothing As It Seems
17. Everything in Its Right Place
18. The Consultant
19. Letters of Transit
20. Worlds Apart
21. Brave New World: Part 1
22. Brave New World: Part 2