A man dies convulsively after being seduced by a woman in a bar. Though a woman clearly entered the room, a man is seen exiting.
Mulder says the death is the fifth of its kind,involving three women and two men who suffered massive coronaries in the throes of passion. Each exhibited huge amounts of pheromones, the essence of animal attraction, containing human DNA-prompting Mulder to describe the killer as 'a walking aphrodisiac' and 'the ultimate sex machine.'
Clues lead the agents to the Kindred, a mysterious and reclusive sect. When one of them, Andrew, touches Scully's hand, she appears shaken. Mulder and Scully meet with the group but are given few answers, after sneaking back to their compound they see one of the members placed in a strange catacomb and revived in a bizarre ritual.
Andrew tells Scully of Brother Martin, one of the Kindred who 'left to become one of you.' He begins to seduce her but Mulder intervenes, at a loss as to what caused Scully to behave so oddly-about to 'do the wild thing.' as he puts it, with a total stranger.
The killer, meanwhile, picks up another potential victim, but is interrupted by a cop. Suddenly, 'she' is a man, punching out the officer and escaping. 'The club scene used to be so simple,' the perplexed victim says in the hospital.
Mulder and Scully track the killer to a motel, finding another body. After a struggle, he/she is caught, but the Kindred spirit him away. 'Humans' Andrew says, 'enjoy pleasures we can't.' A search of their farmhouse later finds the premises vacated, and a large crop circle in the hayfields. 'They're gone,' Mulder says-and by no earthly means of transportation.