S9E3 · Dæmonicus

Following a bizarre double-murder with Satanic ritual overtones in Weston, West Virginia, John Doggett (Robert Patrick) and Monica Reyes (Annabeth Gish) are offered the case. Doggett and Reyes ask Dana Scully (Gillian Anderson) to do an autopsy on the murder victims. The agents come to the conclusion that one of the murder victims was somehow tricked into killing his wife, while evidence at the scene points to two perpetrators. A single clue, the word "Daemonicus", is left spelled out on a Scrabble board the victims had been playing before being attacked. When Reyes claims to have felt the presence of evil, Doggett responds with great irritation. Dr. Monique Sampson calls them, saying that the murders may be connected to an escaped mental patient, Dr. Kenneth Richman, and a guard, Paul Gerlach.

Meanwhile, in a wooded area, the two perpetrators, both wearing demon masks, face each other some twenty paces apart. One of the perpetrators raises his gun and shoots the other. At the mental institution, the two agents interview Josef Kobold (James Remar), the neighbouring patient of Richman. The answers Kobold gives are unsettling for the agents, as he says that one of the perpetrators has killed again, showing them the location and warning them of "something horrible" happening there. After the dead perpetrator's body is recovered, Scully performs an autopsy and discovers that the body belongs to Gerlach.

The agents ask Kobold for help finding the remaining perpetrator. When speaking to Kobold, he suddenly speaks in a strange backward whispering and erupts in convulsions. Reyes hears the word "medicus," meaning "physician." After putting Kobold in the custody of another guard named Custer, Doggett and Reyes race to Sampson's home and find her dead, with a dozen hypodermic needles jammed into her face. During a one-on-one confrontation, Kobold taunts Doggett about his personal life before vomiting all over him. That night, the power suddenly goes out in the mental institution: Custer approaches Kobold's cell and witnesses him turning into a demon.

Doggett phones Scully to tell her that Kobold claims Richman is at an old marina near Annandale, Virginia. Scully drives there, but is attacked by Richman. When Doggett and Reyes arrive, they hear a gunshot from inside an abandoned warehouse. There, they find Richman dead. Scully explains that he was holding her at gunpoint until they arrived, then shot himself. After Scully's lecture to FBI cadets, Doggett explains to her and Reyes that Kobold planned the entire ordeal as a game and got away with it. He explains that the word "Dae/moni/cus" was code for the chosen victims' names, in a game Kobold devised to culminate in his eventual escape from the asylum, and that the "demons" angle was merely to get the X-files' involvement and that they were all thoroughly "checkmated" by Kobold.

Reyes, though accepting of Doggett's theories, is still nevertheless disconcerted with the true feeling of evil that she experienced, and believes Doggett was equally out of sorts because, though loath to admit it, he too felt its presence.