Scully helps Reyes and Doggett investigate a series of bizarre killings that seem to be due to demonic possession but which Doggett believes is a hoax.
In Weston, West Virginia, Darren and Evelyn Mountjoy are playing Scrabble in their home as two men drive up near the house in a pickup. Evelyn lets the barking dog outside while Darren peeks at her letters. The power suddenly goes out and Darren tells his wife to remain there while he goes to get the gun. After he leaves, a hand covers Evelyn's mouth as she is pulled away into the shadows.
Returning with the gun, Darren sees a figure in the dark approaching him. Ignoring his warning not to move, he is forced to fire on the figure. When he comes over, he realizes it is Evelyn, her hands secured with duct tape and her mouth taped over. Kneeling beside her body, he hears eerie whispers from behind him. Two figures emerge from the shadows, their faces monstrous and their intent murderous.
Agent Monica Reyes arrives at the murder scene and goes in to find Darren and Evelyn Mountjoy posed in their chairs at the table with the Scrabble board between them. They are meant to appear as a murder suicide despite it obviously being something else. The word “Daemonicus” appears on the Scrabble board. Reyes seems particularly unsettled by the scene of the crime.
Agent John Doggett enters the house and tells Reyes about the Mountjoy's dog being found with its neck broken outside and the footprints in the mud suggesting two perpetrators. Reyes was called in for her expertise in ritual murder and she agrees that the elements are there: The word being Latin for Satan or demonic possession and the couple being in the murder-suicide pose to suggest they were possessed. Reyes wonders if there isn't something supernatural going on since she felt a feeling as soon as she arrived.
As the people from the coroner's office try and take the body, one of them gets bitten. Pulling open the dead woman's overshirt, Doggett finds two snakes coming out of her two gunshot wounds.
Agent Dana Scully begins teaching at Quantico's FBI Academy and finds Doggett quietly enter the classroom. She performed the autopsies on the Mountjoys. She reveals that the husband killed the wife accidentally, he was then killed in his chair, and the snakes were sewn into the body after the fact by someone with a fair amount of medical experience. Reyes relates to Scully and Doggett that she had worked hundreds of cases like that and this one is different. That she felt she was in the presence of evil when she entered that house. Doggett receives a phone call from a sanitarium claiming their patient was behind the murders.
Doggett and Reyes arrive at Chessman State Mental Hospital in West Virginia and meet with the hospital's chief administrator, Dr. Monique Sampson. Dr. Kenneth Richmond, was committed for sewing strychnine tablets into his patients stomach lining and killing three people that way so Sampson believed it sounded related. He escaped within the last few days. Reyes asks questions about Richmond potentially being possessed or knowing a lot about Satanic ritual but Dr. Sampson doesn't humor Reyes and dismisses it. She does however point out that if they are looking for an accomplice, one of their guards, Paul Gerlach, is missing.
In the woods, the two men from the Mountjoy murders face each other with their demonic masks on. One draws a gun, while the other waits patiently to be shot.
Doggett and Reyes go to see a former Professor, Josef Kobold, in the sanitarium. Doggett tries to convince the man to tell anything he knew about the escape of Richmond from the cell next to Kobold's but Kobold doesn't say anything coherent. He asks Doggett if he can protect him from the Devil. They leave as the conversation proves fruitless.
They are called back hours later to an extremely agitated Kobold, who claims he can lead them to a body based on the dark voices he is hearing.
Driving him out into the woods, Kobold tells them how good it feels to be freed from his cage. He points in a general direction in the woods and Doggett tells the guards to get Kobold “back to his cage.” He believes the man is play-acting as possessed or tormented by demons but in any case, Reyes and Doggett find a dead man hanging upside down from a tree.
When the mask is cut off, they find out that it is Paul Gerlach, the missing guard. Reyes believes that Gerlach could have been a willing host for Satan and that Kobold knows everything since he is tapped into that evil as well. Doggett disagrees. He researched Josef Kobold and learned he was a history professor who ground up six co-eds and used their flesh to fertilize his garden. Reyes wonders why Kobold would still be imprisoned, if he was involved in the crime; he could have escaped with Gerlach and Richmond. Reyes goes to Kobold for help because she believes he can solve the case.
Kobold convinces them to give him a much larger room in exchange for his help. Reyes tells Doggett that even if the man is faking it, they can use him to get information. Kobold tries to get inside Doggett's head by talking about Doggett's son but he refuses to listen to the madman. Then Kobold goes into a seizure and Doggett calls for Reyes.
When Reyes gets to Kobold he says something that suggests Dr. Sampson is in danger.
The murderer drives away moments before the police and the FBI arrive on the scene. They find Sampson with dozens of syringes injected into her face.
Scully informs Doggett that the syringes were filled with the same anti-psychotic that Dr. Richmond was taking. While Scully suggests something strange may be happening, Doggett insists it is like Scully told her class: that most evil in the world is from mankind. He thinks that Kobold has Reyes thinking just the way he wants her to think and now Scully is starting to think that way also.
Doggett attempts to provoke Kobold into revealing that he orchestrated the murders by showing him a paper he wrote years earlier about how the idea of Satan influenced Renaissance thinking. Kobold needles Doggett about Doggett having feelings for Scully that she doesn't reciprocate because he just can't compete with the long lost Mulder. Doggett grabs Kobold and is promptly thrown up on as the man collapses in a pool of vomit.
Scully and Reyes want to test the vomit but Doggett is convinced the man is faking it all, playing a game with them based on his knowledge of Satanic ritual.
Kobold tells the guard, Officer Custer, about where they can find the last body: Happy Landing. When Doggett passes on this information via cell phone, Scully tells him she knows where it is and she is actually near there. She arrives at the old pier first and the others will meet her there. The masked man grabs Scully when she leaves her car.
After they arrive and find Scully missing, Doggett demands Kobold reveal where Scully is and Kobold tells him: “Game’s over, Mr. Doggett. You’ve lost.” A gunshot draws them to an old workshop where they find the masked man dead.
Scully tells them that the man held Scully at gunpoint until they arrived and then he killed himself. Doggett rushes back to the car and sees a fleeing man in patient garb. He shoots him and the man falls off the dock into the water.
After Scully explains to her class that all cases, no matter the evidence, will have some uncertainty and doubt, Doggett and Reyes arrive to talk about her report on Kobold.
Kobold accessed information about all of them through the internet and staged the murders to look like Satanic ritual because he knew they would investigate. Doggett writes DAEMONICUS on the chalkboard and explains that Kobold went to all this trouble to escape while everyone thought he hadn't escaped. That way by the time they started to look for him, he would be long gone.
Doggett found a page from the phone book with Darren and Evelyn Mountjoy circled. They were chosen only because of their names (DA from his and E from hers to form DAE). The second victim was Monique Sampson (MONI) and the final victim was Officer Custer (CUS) who died dressed as Kobold running on the dock.
As Doggett leaves, Reyes explains that there is something that Doggett refused to talk about. Scully asks, “You mean that you felt the presence of evil?” Reyes replies, “No, I mean that he felt it, too.”
- At one point in this episode, a guard named Custer is seen reading a magazine called American Ronin during a thunderstorm. In the Season 3 episode "Pusher", Robert Patrick Modell placed advertisements in the same publication as seen here.
- This episode introduces an alternate version of the Season 9 opening titles that doesn't credit Mitch Pileggi.
- Agent Reyes claims that Dæmonicus means "Satan" in latin. This is entirely false. However she adds it may also refer to "Demon possession" which is closer to the actual definition – Demonic or devilish; belonging to an evil spirit.
- Kobold is German for Hobgoblin
- Gillian Anderson as Special Agent Dana Scully
- Robert Patrick as Special Agent John Doggett
- Annabeth Gish as Special Agent Monica Reyes
- James Remar as Professor Josef Kobold
- Andi Chapman as Dr. Monique Sampson
- Sarah Benoit as Evelyn Mountjoy
- Tim Halligan as Darren Mountjoy
- James Rekart as Paul Gerlach
- Troy Mittleider as Dr. Kenneth Richmond
- Lou Richards as Officer Custer
- Robert Beckwith as First FBI Cadet
- Rueben Grundy as Forensic Technician
- Shane Nickerson as Police Photographer
- Elijah Mahar as Guard