Plot Gary Lambert (Brian Markinson), a telemarketer at an Oak Brook, Illinois, company called VinylRight, believes that his seemingly normal boss, Greg Pincus (John Apicella), is a disguised insect-like monster. Lambert records an audio-taped manifesto and sends it to a radio station, demanding that it be played twenty-four hours a day; on the tape, he claims that the monster, which "hides in the light", stalks employees at VinylRight. The radio station sends the tape to the FBI, where Fox Mulder (David Duchovny) meets with Pincus and lets him hear the audiotape. Mulder takes notice to the phrase "hiding in the light" and calls Dana Scully (Gillian Anderson), asking her to find past X-Files containing the phrase. After one of Lambert's co-workers, Nancy Aaronson (Cynthia Preston), is turned into a living corpse by Pincus—while appearing normal to everyone else—Lambert flees to his apartment and arms himself with an AK-47. He returns to VinylRight and takes Pincus and the other employees hostage along with Mulder. During the situation, Lambert screams out that his boss, Pincus, is a mind-controlling monster and claims that a group of employees are zombies. An alleged zombie, Mark Backus, tries to disarm Lambert only to be shot by Lambert. A Special Weapons and Tactics (SWAT) officer disguised as a cameraman is sent inside to provide agents on the outside with a disposition of Lambert and hostages. Lambert, oblivious to the fact that the camera broadcasts only in a closed circuit mode, tells everyone about Pincus being a monster. The lights are cut, but before the SWAT team moves in Lambert forces Mulder to look behind him. Mulder hears a clicking sound and looks at Pincus who, for an instant, appears to be a large insect. Just then, the FBI break into the room, and kill Lambert before he can open fire. At Lambert's house, Mulder finds a map of Pincus' movement over the years, which corresponds to other cases of psychotic breaks. He then notices Nancy Aaronson, the co-worker Lambert saw as a zombie, through a window looking like a corpse. Elsewhere, the forensic pathologist tells Scully that the corpse of Mark Backus appears to have been dead for two to three days, although the man had been killed only hours before. At the house of a different female employee, Gretchen Starns, Mulder looks through the window, sees the beast and hears a loud scream. Mulder breaks the window and then kicks in the door. Behind him, out of his sight, the beast walks across the ceiling. Mulder catches a glimpse of it crawling up the outside of the house. Later at the FBI, Pincus complains to Assistant Director Walter Skinner (Mitch Pileggi), but Mulder, seeing Pincus begin to transform into the creature again, draws his weapon. He is restrained by a disbelieving Skinner and then sedated in a hospital. Mulder claims that the creature bit the back of the employee's head. Scully re-examines Mark's corpse and finds three puncture marks at the top of the spine marking the corners of an equilateral triangle. In the hospital, Mulder is restrained in his bed and sees the silhouette of the beast at the window. He screams for the nurse, who has been bitten by Pincus. Scully, however, goes to visit Mulder. The nurse refuses access, but, for a moment, Scully sees her as a corpse. Scully runs into Mulder's room, sees the beast on the wall over Mulder, and shoots at it. It leaps through the partially open window, breaking the glass and wooden frame. Scully testifies to Skinner that she believes Mulder is fit for duty, noting that Pincus and several others mysteriously disappeared, there was an intruder in Mulder's room, and that Mark did have some sort of chemical in his system. She explains that the two of them had a Folie à deux—a madness shared by two. The episode ends with a different man at telemarketing agency noticing the same ominous signs of the creature.