When a man is killed in exactly the same way that aliens mutilate cattle, Mulder is fascinated that aliens may be bored with animals and are starting on humans.

After interviewing the family of the man who was killed, Mulder and Scully travel across the country to investigate what sounds like an identical murder. Mulder suspects aliens but Scully thinks that there are two very clever serial killers at large. It is only when they meet the family of the next murdered man that M & S uncover some more troubling questions. Namely, how can the two daughters of the different families be completely identical and what would be the odds in Vegas for both their fathers to be killed at exactly the same time in exactly the same fashion?

But when both girls are kidnapped, Mulder thinks that a serial killer is casually doing away with their families. A tip off from Deep Throat informs Mulder of a woman named Eve 6 who is currently locked up in a high security prison. The two agents find out that a series of experiments by a Dr. Sally Kendrick (Harriet Harris) to clone human beings and call the boys Adam and the girls Eve have been successful apart from one thing. The clones are basically very clever pyschopaths.

This is shown when the two girls murder their kidnapper, Sally Kendrick by poisoning her. M & S (suspecting nothing) look after the girls and almost become victims themselves if it were not for Mulder. The Eve's are locked up in the same prison as Eve 6 until the arrival of Eve 8......