Four African-American men have vanished off the streets of Philadelphia. An FBI/Police task force has come up with no leads...until the body of the most recent victim is discovered. Surprisingly, violence isn't the cause of death. The body's bizarre lack of pigmentation hints at some unknown ailment. The Centers for Disease Control calls in Scully to unravel the medical mystery.

     Mulder, however, believes that more than a simple pathogen is involved. His investigations lead to a cover-up of a similar death on a flight from West Africa, and the presence of a toxic plant native to that area. Meanwhile, Scully discovers that the victim's pituitary gland-- which produces melanin among other hormones--has somehow been destroyed.

     While their investigation is under way, the killer strikes again. This time a young black student is stalked and kidnapped from a bus stop. The evidence leads Scully and Mulder to a recent West African immigrant, Samuel Aboah. They arrest him when he attempts to escape. Hospital tests reveal that, among other peculiar abnormalities, Aboah lacks a pituitary gland.

     A tip from his UN informant sends Mulder to Minister Diabira, a diplomat from the West African country of Burkina Faso. Reluctantly, Diabria admits he had ordered the cover-up of the first murder -- because he knew the identity of the killer. It was one of the mythical Teliko: evil spirits of the air, who emerge at night to suck the life and color out of their victims. Who would have believed that a terrifying West African folktale could come to life in 20th century America? No one...except Mulder.

     Mulder explains his theory to a skeptical Scully: the Teliko are not ghostly entities, but members of a lost African clan, who have survived over generations by hunting down other humans to steal what they lack: hormones from the pituitary gland.