"Letters of Transit" is the nineteenth episode of the fourth season of the Fox science-fiction drama television series, Fringe, and the series' 84th episode overall. It is set in the future, where the Observers have taken control of human society. In 2036, two FBI agents fight to free their world of the Observers by finding the amber-encased bodies of the original Fringe team. The episode's premise is subsequently built upon as the key setting of the show's fifth and final season.