The Pine Bluff Variant

"The Pine Bluff Variant"
The X-Files episode
The effects of the biological weapon, which causes rapid degeneration of human flesh. The special effects and mood for the scene were critically applauded.
Episode no.	Season 5 Episode 18
Directed by	Rob Bowman
Written by	John Shiban
Production code	5X18
Original air date	May 3, 1998
Running time	45 minutes
Guest appearance(s)
Daniel von Bargen as Jacob Haley J.B. Bivens as Field Agent Armin Moattar as Goatee Man Sam Anderson as Leamus Michael MacRae as August Bremer Kate Braidwood as the Usherette Ralph Alderman as the Manager Trevor Roald as Martin Kett Turton as Brit Douglas Arthurs as Skin-Head Man John B. Lowe as Dr. Leavitt Michael St. John Smith as the CIA Operative
Episode chronology
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List of The X-Files episodes

"The Pine Bluff Variant" is the eighteenth episode of the fifth season of the American science fiction television series The X-Files. It was written by John Shiban and directed by Rob Bowman. The episode aired in the United States on May 3, 1998 on the Fox network. The episode is a "Monster-of-the-Week" story, a stand-alone plot which is unconnected to the series' wider mythology, or fictional history. "The Pine Bluff Variant" received a Nielsen household rating of 11.4 and was watched by 18.24 million viewers in its initial broadcast. It received largely positive reviews from television critics as well as fans on the internet.

The show centers on FBI special agents Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson) who work on cases linked to the paranormal, called X-Files. In this episode, Scully grows suspicious of Mulder when she thinks he may be helping a terrorist organization. Scully begins to wonder if he is now a traitor to the FBI. It is eventually revealed that Mulder is working as a mole in the group, and he is trying to stop them before they are able to use a biological weapon—that may have been created by members of the US government—which causes rapid degeneration of human flesh.

"The Pine Bluff Variant" was based on the idea of Mulder going undercover, a topic that Shiban had wanted to work on for a majority of the fifth season. Shiban argued that the conceit worked for the series because the theme of Mulder questioning his beliefs was a major element of the fifth season. The episode was indirectly influenced by the 1963 novel The Spy Who Came in from the Cold, written by John le Carré. The title is also a reference to the Pine Bluff Arsenal, a real United States military base with stockpiles of chemical weapons.