A father and son shoot a fierce-looking beast that, on closer inspection, turns out to be a Native American man. During the frenzied encounter the son, Lyle Parker, is wounded by the creature before it's killed.
Mulder and Scully are told that the rancher's cattle have been slaughtered, and that the Parkers have been involved in a boundary dispute with the local reservation. A look at the dead man's corpse, meanwhile, reveals wolf like fangs.
Mulder explains that this same region was involved in "the first X-File, initiated by J. Edgar Hoover himself," stemming from a series of murders in 1946 by a vicious animal. Although a suspect was killed, the murders resumed in 1954, '59, '64, '78,' and now '94, and Mulder says that even the Lewis and Clark expedition "wrote of Indian men who could change into a wolf."
The older Parker is subsequently ripped to pieces on his porch, with Lyle found nude and unconscious nearby. Scully takes him to hospital, while Mulder visits with a tribal elder who tells him what happened in 1946 and the legend of the Manitou- an evil spirit capable of changing a man into a beast.
Mulder calls the hospital, learning that Scully has taken Lyle Parker back to his ranch and that traces of his father's blood were found in his stomach-traces that could have only gotten there via ingestion. As night falls, Mulder and the sheriff hurry to the ranch, arriving just in time to shoot a creature that, in fact, is Lyle Parker.
The tribal elder provides the cryptic coda. "FBI," he says. "See you in about... eight years."