"Eve" is the eleventh episode of the American science fiction television series The X-Files, premiering on the Fox network on December 10, 1993. It was written by Kenneth Biller and Chris Brancato, directed by Fred Gerber, and featured guest appearances by Harriet Sansom Harris and Jerry Hardin in his role as Deep Throat. The episode is a "Monster-of-the-Week" story, unconnected to the series' wider mythology. "Eve" earned a Nielsen household rating of 6.8 and was watched by 6.4 million households in its initial broadcast. It received positive reviews from critics.

The show centers on FBI agents Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson) who work on cases linked to the paranormal, called X-Files. When Mulder and Scully investigate two seemingly identical murders that occurred simultaneously thousands of miles apart, they find that both victims' daughters may be the product of a secret human cloning project created by the government.

The episode was pitched to series creator Chris Carter by freelance writers Biller and Brancato under the title of "The Girls from Greenwich", with the focus being on genetic experiments conducted on sets of twins. The producers initially looked for twins to play the roles of Teena and Cindy in Los Angeles, but child labor laws made using children from there so difficult that they instead searched locally in Vancouver, finding Erika and Sabrina Krievins.

In Greenwich, Connecticut, a jogging couple find their neighbor, a young girl named Teena Simmons, standing alone in her driveway. After she explains her father is in the yard, the couple find him sitting dead on a swing set with two incisions in his neck. When FBI agents Fox Mulder and Dana Scully take the case, Mulder explains that he believes the death is an example of extraterrestrial cattle mutilation on a human being. The agents meet Teena, who claims to have seen "red lightning" when her father died and that "men from the clouds" had wanted to "exsanguinate him."

Leaving Teena in the state's care, the agents travel to Marin County, California, where a similar death has occurred at the Reardon residence. Mulder and Scully realize that, despite thousands of miles lying between the two crime scenes, the killings were committed on the same day and at the same moment. Meanwhile, back in Connecticut, Teena is kidnapped by a dark-clothed figure.

When Mulder and Scully meet Mrs. Reardon and her daughter, Cindy, they discover that Cindy is completely identical to Teena. Cindy's mother tells the agents that her daughter was conceived via in vitro fertilization at a fertility clinic in San Francisco. There, Scully learns that both the Simmonses and the Reardons were treated by Dr. Sally Kendrick, who was eventually fired for conducting eugenics experiments with ova from the clinic's lab. Meanwhile, Mulder is contacted by Deep Throat, who details a Cold War-era supersoldier program that produced genetically modified clones who were identified as "Adam" or "Eve" based on their sex. Deep Throat tells Mulder of a woman connected with the project who is currently kept in a mental hospital.

Mulder and Scully travel to the hospital and meet "Eve 6", who bears an identical resemblance to Sally Kendrick. Eve 6 tells them that the Adam and Eve clones created for the program had extra chromosomes which led them to display superhuman intelligence and strength, as well as extreme homicidal psychoses. The last three Eve clones—Eves 6, 7, and 8—were institutionalized after the project was cancelled. However, Eve 7 escaped and later joined the fertility clinic as "Sally Kendrick", modifying the ova of the clinic's patients to create new Eve clones. Eve 8, who also escaped, is still at large.

Though Mulder and Scully place Cindy's house under surveillance, they're unable to prevent one of the escaped Eves from abducting Cindy. The Eve takes Cindy to a motel where Teena is already being held captive and introduces the two girls to each other. The woman reveals herself to be Eve 7/Sally Kendrick and explains that she cloned the girls using her own genetic material to improve upon the original program's flaws, only to learn about the girls' "accelerated development" after they murdered their fathers. She asks the girls how they learned of each other's existence and how they planned the murders, to which they reply that they "just knew." The girls poison Eve 7's drink with a fatal dose of foxglove.