In , titled "Brave New World: Part 1," the Fringe team faces a catastrophic event where victims spontaneously combust due to nanotechnology. This episode serves as the first half of a two-part season finale, originally produced to potentially conclude the series. Key Plot Points
: A device planted in a public escalator releases nanites into riders, causing them to ignite if they move. Watch www xrysoi se Fringe S04E21
: While investigating a warehouse linked to Bell, Astrid is shot by a henchman. As Walter tends to her, William Bell himself appears, confirming Walter's suspicion that he is alive. Why It's a "Must-Watch" Episode In , titled "Brave New World: Part 1,"