This week's episode is titled "Northwest Passage", where a murder investigation linked to Thomas Newton has Peter helping the local authorities solve these murders. The man from the Other Side also makes an appearance.
This is a very unusual episode of Fringe. Anxiety caused by Peter's disappearance leads Walter to smoke some funky marijuana. Walter then tells Olivia's niece a story, and his imagination becomes the setting for a musical mystery put on by the rest of the Division.