Peter is easily the most memorable episode of Fringe, in part because it illuminated so many details of a storyline which had been hinted at since the first season, but mainly because it was such a daring episode for the series. The tale of Walter's abduction of Peter from the parallel universe is told in an 80s flashback, indicated by the fun retro title sequence and huge mobile phones. The episode packs in plot development, pathos and humour while jumping between universes, as only Fringe can. It's tragic that so much of Peter's kidnapping is accidental. Walternate almost synthesises a cure for his son, but is distracted by September, so a grieving Walter replicates it. He's almost stopped by Nina Sharp, who foresees the damage caused by a door between universes, and the cure is smashed. Peter must be brought back to our world, where Walter realises that he can't return him, both because of the damage he's caused and because he can't lost him again. The episode introduces us to Peter's mother Elizabeth, whose grief is devastating though we barely know her, and also to Walternate, who is tellingly not entrusted with his Peter's coin as Walter is in the prime universe. However, the episode belongs to Walter himself, who is so sadly adamant that he must accept that Peter will live happily elsewhere, only to find himself unable to watch his son die again. Peter sets up the emotional core of the series so perfectly that it still packs a punch years after it first aired.
