"Tunguska" is the eighth episode of the fourth season of the American science fiction television series The X-Files. It premièred on the Fox network on . It was directed by Kim Manners, and written by Frank Spotnitz and series creator Chris Carter. "Tunguska" featured guest appearances by John Neville, Nicholas Lea and Fritz Weaver. The episode helped explore the series' overarching mythology. "Tunguska" earned a Nielsen household rating of 12.2, being watched by 18.85 million people in its initial broadcast. In the episode, FBI special agent Fox Mulder (David Duchovny) travels to Russia to investigate the source of a black oil contamination. His partner Dana Scully (Gillian Anderson) and assistant director Walter Skinner (Mitch Pileggi) are summoned to attend a United States Senate hearing on Mulder's whereabouts. "Tunguska" is a two-part episode, with the plot continuing in the next episode, "Terma". "Tunguska" was inspired by reports of evidence of extraterrestrial life possibly being found in the Allan Hills 84001 meteorite, while the gulag setting was inspired by the works of Aleksandr Solzhenitsyn. The story offered the writers a chance to expand the scale of the series' mythology globally, although production of the episode was described as troublesome and expensive. Plot The episode opens in medias res to Dana Scully (Gillian Anderson) as she is brought before a Senate select committee to be questioned about the whereabouts of Fox Mulder (David Duchovny). Scully refuses to answer the committee's questions and attempts to read a statement denouncing the conspiracy within the government. Senator Sorenson threatens to hold Scully in contempt of Congress. Ten days earlier, at Honolulu Airport, a courier returning from the Republic of Georgia (David Bloom) is searched by customs officers. One of the officers (Andy Thompson) removes a glass canister from the courier's briefcase and accidentally shatters it, exposing both men to the black oil. Meanwhile, in New York City, Mulder and Scully take part in an FBI raid against a domestic terrorist group. Mulder's tipster within the group is revealed to be Alex Krycek (Nicholas Lea), whom the terrorists released from the missile silo where he had been trapped. Krycek has turned against The Smoking Man (William B. Davis), and tells the distrustful agents that he can help expose him. Krycek leads the agents to Dulles International Airport, where they try to apprehend a second courier carrying a diplomatic pouch from Russia. The courier leads the agents on