Folie à Deux

Gary Lambert, an employee of the VinyRight call center in Chicago, begins to hear a strange chirping at work. Later, he sees the image of a giant insect in the place of his boss Greg Pinkus. Later, Pinkus calls Gary's colleague Nancy Ayranson to the office. Gary sees his returning colleague as a half-decomposed corpse. In the end, Gary records a message about the existence of a monster with death threats, sends it to the radio and calls for it to be played every hour.

Walter Skinner assigns Mulder and Scully to this case, but Mulder goes alone, believing that the case is not worth wasting his partner's time. At the company VinyRight, there have already been incidents related to the strange behavior of employees. Once an employee even started threatening with a gun. Mulder goes to Pinkus, who lets him listen to a recording made by Lambert. Mulder parses the words "hiding in the light" in the recording and asks Scully to look through old files for the mention of these words. Meanwhile, Lambert finally goes crazy and, armed with a Kalashnikov assault rifle, decides to destroy the monster, and at the same time show it to the world. Scully reports that the words "hiding in the light" were mentioned in a 1992 case: a local priest, Gerald Resnick, then uttered these words to a Lakeland, Florida police investigator. Gerald claimed that there was a creature among the parishioners that only he could see. One day he came to Mass with four pistols and started a massacre, and then committed suicide. Mulder agrees that he could use Scully's help.

Maledr visits VinyRight's office again, but finds himself among the hostages taken by Gary Lambert. He wants to get access to television in order to show the whole world the "monster" – Greg Pinkus. Of course, the monster, as well as the "zombified" employees of the company, is seen only by Gary himself. Scully arrives at the place where the special forces, led by Agent Rice, are already working. Mulder tries to pull his gun out of its holster, but due to a call from Agent Rice, it is revealed. At this moment, an employee of the company, Mark Backus, tries to attack Lambert, but Harry kills him. After that, he begins to argue that Mark was already a walking corpse, which means there is nothing wrong with killing him. At Lambert's request, an operator is brought to the office to shoot a video message. Gary wants to shoot Greg on camera, but Mulder stands in front of him. The lights go out in the building. Gary convinces Mulder to turn around and look at Greg. Turning around, Mulder sees a terrible monster in Pinkus' place. At this moment, an armored personnel carrier breaks through the wall, and the special forces who broke in immediately kills Lambert.

Mulder interrogates Pinkus and finds out that he has been in cities where similar incidents have occurred in the past, including the case in Lakeland. This leads Mulder to believe that Gary was telling the truth. Scully also believes that Mulder experienced stress, which caused the so-called "Folie à deux", that is, similar delusions observed in two people. Mulder asks for an autopsy on Mark Backus' body for him, but Scully refuses. Together with Agent Rice, Mulder goes to Lambert's house, where it turns out that he also tracked similar cases. Outside the window, Mulder sees a zombified Nancy Airanson and immediately begins a chase, but she manages to hide in Pinkus' car.

Skinner wants to find out from Scully what is the reason for Mulder's strange behavior and why he returned to Chicago. Scully hesitates to say that Mulder took Gary's words for the truth. Later, Scully examines Backus' body and discovers that he died at least a day before Lambert was shot. Meanwhile, Mulder follows Pincus' car and gets to the house of a VinyRight employee, Gratchin Starnes. Through the window, Mulder sees an insect-like creature approaching a woman watching TV. Fox breaks the window, but the creature hides. After knocking out the door, Mulder discovers only the zombified body of a woman and screams about a monster. Skinner, Pinkus and the seemingly normal Starnes are trying to figure out the situation. Mulder tells what he saw, but Skinner thinks Fox has gone mad. Starnes leaves, leaving Pinkus alone with Skinner and Mulder. Pinkus forgives Mulder, believing that he has experienced stress, and promises not to go to court. At this moment, Mulder sees that Pinkus turns into an insect with a sting and tries to attack Skinner. Fox grabs the gun, but Skinner stops him.

Mulder is placed in a psychiatric hospital. Meanwhile, Scully, during a re-examination, discovers traces of the monster's sting on Bakus' body. An insect-like creature sneaks into Mulder's room through the window. A nurse comes running to the screams and shows that there is no one outside the window. She leaves it open, stating that Mulder needs fresh air. At this moment, blood is visible on the back of the sister's neck, which indicates that she is also under the control of the creature. Scully arrives to visit Mulder and sees that the nurse is a zombie. At the moment when the creature almost attacks Mulder, Scully bursts into the room and shoots a gun. The creature breaks the window and falls out into the street, which suggests that it was real all the time.

Scully reports to Skinner that he believes Mulder's mental health is stable, and also reports punctures on Bakus' body and the disappearance of Pinkus, along with six employees of the company, whom Lambert previously described as zombies, and nurses. In the finale, another employee of the company VinyRight hears chirping sounds and informs the client that "it's here."