The K Files investigates the conclusion to Nisei: 731. Mulder does his usual move of jumping on a train carrying a human-alien hybrid and gets embroiled in a tense sequence with an NSA Agent. Meanwhile, Scully gets closer to uncovering the truth about her abduction.

731 is a stunt heavy episode (especially for Duchovny) not mention a massive practical explosion of a retired railway car. The episode snagged series director of photography, John Bartley, an American Society of Cinematographers award nomination, and also propelled Bowman toward directing the series' subsequent film adaptation, The X-Files.