The fourth season of the American science fiction television series The X-Files commenced airing on the Fox network in the United States on October 4, 1996, concluding on the same channel on May 18, 1997, and contained 24 episodes. Following the filming and airing of the season, production began on The X-Files feature film, which was released in 1998 following the show's fifth season. The fourth season of the series focuses heavily on FBI federal agents Fox Mulder's (David Duchovny) and his partner Dana Scully's (Gillian Anderson) investigation of an alien conspiracy, which is protected by the mysterious Syndicate. Midway through the season, Scully is diagnosed with terminal cancer, a result of her previous abduction, and Mulder begins to lose his faith in the idea of extraterrestrials. Debuting with high viewing figures and ranking as the twentieth most watched television series during the 1996–97 television year in the United States, the season was a success, with figures averaging around 20 million viewers an episode. This made it, at the time, the highest rated season of The X-Files to air. The season's twelfth episode, "Leonard Betts", was chosen as the Fox lead-out program following Super Bowl XXXI, and was viewed by 29.1 million viewers, making it the highest-rated episode in the series' run. Critical reception from television critics was mostly positive. Plot overview 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. When the Syndicate suspect that one of their members is passing information to Mulder and Scully, they organize a canary trap to find the leak, using information about the safety of Mulder's mother as bait. X's (Steven Williams) role as an informant is discovered, and he is shot dead, although he is able to pass along the name of another informant who can be of use to Mulder—Marita Covarrubias (Laurie Holden), the Special Representative to the Secretary-General of the United Nations. Covarrubias' aid is sought when Mulder attempts to reach Tunguska in Russia to investigate the source of a further black oil contamination. Whilst there, Mulder is held in a gulag and used as a successful test subject for a black oil vaccine. He escapes and is able to return to America, having found that Alex Krycek (Nicholas Lea) is working with the Russians. Having been diagnosed with cancer, Scully is unsure