Stephen Root plays a key role on this episode of Fringe.
The Fringe team works against time to try to keep it from devouring people in its wake.
Peter's return and a brilliant physicist and her husband have discovered a way to go back in time, and Peter's return triggered the event.
Walter is still struggling with the appearance of Peter, "the object."
Olivia has no interest in Peter, but recognizes a version of herself was of importance to him.