Subject 13 (Fringe)

"Subject 13" is the 15th episode of the third season of the American science fiction drama television series Fringe, and the 58th episode overall. Inspired by fan reaction to the show's previous flashback episode, "Peter", "Subject 13" occurs 25 years before the show's current timeline, in 1986 six months after "Peter". The episode, with scenes set in both the prime and the parallel universe, explores Walter and Elizabeth Bishop's attempts to return Peter to the parallel universe using the Cortexiphan-induced abilities of young Olivia Dunham, while Walternate in the parallel universe struggles to deal with the kidnapping of his son.

Showrunners Jeff Pinkner and J. H. Wyman, as well as consulting producer Akiva Goldsman wrote the episode, while producer Frederick E. O. Toye worked as the director. Guest actress Orla Brady returned to reprise the role of Elizabeth, while Chandler Canterbury, Karley Scott Collins, and Chris Bradford made their first guest appearances. On its initial broadcast in the United States on February 25, 2011, an estimated 4.0 million viewers tuned in. Critical reception to the episode was overwhelmingly positive. It was ranked the third best episode of the entire series by Entertainment Weekly.