Truer words have never been spoken.
What we have here is a locked room mystery. Three killings, the latest being a Baltimore business, have all ended in a devoured liver and no plausible ingress or egress. The FBI agent in, charge, Tom Colton, asks Scully for help in getting Mulder to take a look, which he does, after talking about the Reticulians' need for more iron in their diet.
Mulder, having access to the X-Files, notices that similar killings took place in both the 30s and the 60s, displaying a 30 year pattern. The crime scene does have some evidence: a very elongated fingerprint, which is also similar to the previous crimes. They also contained five murders each; Mulder warns everyone that the killer isn't finished.
Scully, uses textbook FBI teaching, believes the killer will return to the scene of his previous crimes. Mulder is skeptical, but they wind up catching a man named Eugene Tooms crawling through the vents. His story is that he works for a pest control company and had been sent out, a fact corroborated by his work place. He passes a polygraphy test with flying colors, but when Mulder takes his fingerprints and elongates them, they are a perfect match for the print found at the crime scene. He is, of course, dismissed out of hand, since he explains that Tooms can obviously elongate his body at will. Fortunately, no one makes the inevitable dirty jokes that Mr. Fantastic always has to deal with.
No one dared make Santa jokes either...
Meanwhile, Tom Colton proves his worth as an agent by ignoring Mulder after asking his advice. Scully points this out, and shouts at him quite a bit.
Mulder and Scully can find no information on Tooms, and they find out that he has not returned to work since being released from custody. They find the retired detective that worked on the first case, and even though he was dismissed from the 60s case, gathered up enough evidence (including photographs) on his own to show that Tooms is the same man, still living in the same apartment. He also says something about "pure evil".
Our heroes investigate Tooms' apartment, and find a crawlspace turned into a nest of newspapers and bile, with trophy items to, you know, decorate. Yes, it is just as creepy as it sounds.
"Is there any way I can get it off my fingers quickly without betraying my cool exterior?"
And as they leave, Tooms secretly steals Scully's necklace.
That night, Tooms gets into Scully's apartment through a tiny vent, and if seeing his arm slowly stretch longer and longer did not freak you out, you are stone, my friend, stone.
Mulder goes back to watch the apartment even though Colton demanded he stay away from the case. he finds Scully's necklace in Tooms' trophy nest. He gets back to Scully's apartment just in time to prevent her from not having a liver anymore.
Tooms is locked up in a room without vents. But, quite unfortunately, there is this very tiny slot they use to shove food through...
Sleep well, everyone.
This episode was pure, unadulterated nightmare fuel and that is high praise.