MULDER BOARDS A TRAIN CARRYING A BOMB AND A MYSTERIOUS QUARANTINE SUBJECT AS SCULLY LEARNS MORE DETAILS OF HER ABDUCTION.
At a remote leper colony in West Virginia, leprosy victims watch in hiding as other patients are rounded up by a death squad and systematically murdered. Aboard a speeding train, Mulder searches for the Japanese doctor in charge of the mysterious being he saw loaded on a quarantine car -- a doctor whom Scully identifies from photographs as having been present during her abduction. When Mulder finds the man garroted in a bathroom, he goes in search of the killer still on the train. Scully links the Japanese doctor to a West Virginia leper colony, and discovers a mysterious informant with a tale of human medical experimentation dating back to World War II. Mulder's belief in alien hybridization experiments is tested against Scully's conviction that the evidence points to extensive medical atrocities. Only Scully's memories and cryptic messages from X can save Mulder who is trapped in a sealed train car with a bomb, a cold-blooded killer, and an occupant who may or may not be a human/alien hybrid.