"Unusual Suspects" is the third episode of the fifth season of the American science fiction television series The X-Files and the 100th episode overall. It was written by Vince Gilligan and directed by Kim Manners and it originally aired in the United States on November 16, 1997 on the Fox network. The episode earned a Nielsen household rating of 13.0, being watched by 21.72 million people in its initial broadcast and received mixed to moderately positive reviews from critics.

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. "Unusual Suspects", however, functions as a flashback episode: in 1989, two salesmen and a federal employee join forces when they meet Susanne Modeski, a woman who claims that she is being pursued by her supposedly violent ex-boyfriend, an FBI agent named Fox Mulder. A sequel to the episode was later filmed during the series' sixth season, entitled "Three of a Kind".

The concept for having an episode dedicated to The Lone Gunmen arose when the show's producers were forced to start production of the fifth season in the last week of August in Vancouver, but still needed series stars David Duchovny and Gillian Anderson for the filming of The X-Files movie in Los Angeles. Duchovny appears in a reduced capacity in the episode, while Anderson is absent entirely. Writing duties fell to Vince Gilligan, who initially drafted a story about nanotechnology, before changing to the origins of The Lone Gunmen on behest of series creator Chris Carter. In addition, "Unusual Suspects" serves as a cross-over with the NBC series Homicide: Life on the Street, featuring Richard Belzer's Detective John Munch character.

The episode opens in medias res in 1989, when a SWAT team conducts a raid on a Baltimore warehouse. Inside, they find a naked and disoriented Fox Mulder in a box, shouting, "They're here!" Three men attempt to flee the scene and are captured; they are revealed to be the Lone Gunmen. As they sit in a city jail, they begin blaming each other for the predicament they have found themselves in. Detective John Munch interrogates John Fitzgerald Byers, who tries to explain what happened.

In the flashback, Byers, a public affairs officer for the FCC, attends a computer and electronics convention. There, he follows a beautiful woman who passes his booth; he also passes by booths manned by Melvin Frohike and Richard Langly, who are both selling stolen cable television. When Byers bumps into the woman, she introduces herself as Holly and claims that her daughter had been kidnapped by her ex-boyfriend, who is in the Baltimore area.

Holly possesses a piece of paper with "ARPANET/WHTCORPS" written on it. Byers realizes that the words refer to the Defense Department's computer network, which she requests he hack into. Byers, at the time an unquestioningly loyal government employee, reluctantly complies. He finds an encrypted file on her daughter, named Susanne Modeski. Just then, a man whom Holly claims to be her boyfriend passes by Byers's booth. It is Mulder.

Byers and Holly recruit Frohike to help them decipher the file. Both Byers and Frohike decide to assault Mulder, but they decide not to when he introduces himself as an FBI agent. Returning to his booth, Byers finds his FCC colleague being arrested for the hacking Byers committed. Frohike convinces Byers not to turn himself in, and recruits Langly to help them hack into the FBI database to learn more about Holly. They discover that "Holly" is actually Susanne Modeski, who is wanted for acts of murder, sabotage, and terrorism at a weapons facility in New Mexico.

Susanne admits her deception but claims that she was scapegoated for trying to leave her job at the weapons facility. There, she had been working on ergotamine, an aerosolized gas that causes paranoia and anxiety. Susanne claims that the government plans to test the gas on civilians in Baltimore. After deciphering the file, the Lone Gunmen find that she was telling the truth, learning the location of the gas. Susanne also finds evidence that she had a tracking device put in a tooth, which she pulls out.

The four of them head to the warehouse, where they find the gas stored inside asthma inhalers. Mulder arrives to arrest them, but two dark-suited men come to take Susanne. They fire at Mulder, hitting the boxes behind him and exposing him to the gas. The exposure causes Mulder to strip naked, hide in the box, and hallucinate about seeing aliens in the warehouse. Susanne shoots the men and escapes. More men then arrive, led by X, who intimidates the Lone Gunmen to attain their future silence. Byers confronts X, asking him about his actions and mentioning the supposed cover-up of the John F. Kennedy assassination. X's unconvincing denial — "I heard it was a lone gunman" — becomes the origin of the trio's name. X leaves, just as the police arrive and arrest the Lone Gunmen.

Detective Munch does not believe Byers's story, but it is soon corroborated by Mulder. After the Lone Gunmen are released, they encounter Susanne after she has failed to get the press to believe her story. She tells them to reveal the truth to as many people as possible. Susanne is then captured by X, who leers at the Lone Gunmen as he departs with her. Later, the three of them meet Mulder in the convention center and explain what happened to him.^[1]

"Unusual Suspects" premiered on the Fox network on November 16, 1997.^[7] This episode earned a Nielsen rating of 13.0, with a 19 share, meaning that roughly 13.0 percent of all television-equipped households, and 19 percent of households watching television, were tuned in to the episode.^[8] It was viewed by 21.72 million viewers.^[8]

The episode received mixed to moderately positive reviews from critics. The A.V. Club reviewer Emily VanDerWerff gave "Unusual Suspects" an A−, and wrote that the episode "is a love letter to the very idea of paranoia".^[9] Furthermore, VanDerWerff argued that "as the episode moved its way to its climax, when Mr. X improbably lets the Gunmen live after seeing as much as they did ... it struck me that what we're seeing here may not entirely be meant to be taken seriously, just as 'Memoirs Of A Cigarette Smoking Man' [sic] is more about who the CSM wished he might have been than the person he actually was. This isn't a true story; it's a manifesto."^[9]

Robert Shearman and Lars Pearson, in their book Wanting to Believe: A Critical Guide to The X-Files, Millennium & The Lone Gunmen, rated the episode three stars out of five. The two compared the episode to "Musings of a Cigarette Smoking Man", but called it "throw away and charming".^[10] Shearman and Pearson criticized the episode for being "largely concerned in suggesting to the audience that the government is being conspiratorial ... five seasons into a hit series which has turned that argument into a cliche."^[10] Paula Vitaris from Cinefantastique gave the episode a positive review and awarded it three stars out of four.^[11] She wrote that, "'Unusual Suspects' is filler–but amusing filler".^[11] Vitaris further complimented the performance of Signy Coleman as Susanne Modeski, and called the return of "not-yet-dead" X as "welcome".^[11]