S4E20 · Small Potatoes

Agents Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson) investigate the birth of five babies in the town of Martinsburg, West Virginia, who were born with tails. The mother of the most recent baby, Amanda Nelligan, tells the agents that the father of her baby is Luke Skywalker. By researching the baby's chromosomes it is discovered that all five share the same father. The parents of the children blame the local fertility doctor, who had used insemination to impregnate all of the mothers but Nelligan. Mulder spots a janitor nearby with signs that he formerly had a tail. When he runs, Mulder chases him and catches him. The janitor, Eddie Van Blundht, is discovered to be the father of all of the children. Scully believes Eddie used a date rape drug although Mulder questions how he could be in the position to give it to the women.

Eddie escapes by transforming his face into that of the booking cop and knocking him out with a blow to the head. Mulder and Scully visit Eddie's father, a former circus performer who claims he still has his tail. Mulder and Scully soon realize the father is actually Eddie when he addresses Mulder by name without having been introduced. The agents give chase, but Eddie escapes. He then transforms into the husband of a woman he impregnated and hides out in their house. When the real husband comes home early, Eddie transforms into Mulder and leaves the couple confused. Mulder and Scully meanwhile discover the desiccated remains of Eddie's father hidden in the attic. Performing an autopsy on the body, Scully finds that he had an extra sheet of muscle under his skin, which Mulder concludes Eddie inherited and uses to transform his appearance.

As Mulder, Eddie visits Nelligan, showing her a photo of Eddie. Nelligan tells him that she went out with him in high school, but views him as a loser lacking drive and ambition. The disappointed Eddie leaves just as the real Mulder shows up. Realizing that Eddie just visited Nelligan in his guise, Mulder searches for him down the hospital corridors. He finds the fertility doctor and a security guard nearby and handcuffs them to each other, believing one of them to be Eddie. The real Eddie, however, is hiding in a vent above. He gets the jump on Mulder and locks him up in the hospital basement. Again as Mulder, Eddie tells Scully that he feels the case is a waste of time and they should return to Washington.

Eddie returns to Washington as Mulder with Scully and presents the case to Skinner with a poorly written report. Eddie visits Mulder's office, then his apartment, being surprised at what a loser Mulder appears to be (though highly pleased with how attractive a man he now is in Mulder's face - as he admires himself and practices his 'agent moves' in the mirror). Later that evening, Eddie visits Scully with a bottle of wine and tries to get her drunk and seduce her. As a reluctant Scully is about to give in to a kiss, the real Mulder breaks in and interrupts them.

Revealed, Eddie sheepishly reverts to his actual form, shocking Scully. A month later, Mulder visits Eddie in prison. Eddie complains at being given muscle relaxants to prevent him from turning into someone else, asking if that was Mulder's doing. Eddie then tells Mulder that he was born a loser, but Mulder is one by choice and that he should seriously "live a little".