At a state penitentiary, psychiatrist Dr. James Martin arrives to evaluate a notorious serial killer named Edward Wayne Brady, who is currently a death-row inmate. The prison Warden Tom Moss warns Dr. Martin, who has just replaced Dr. Alan Fischer who committed suicide after previously interviewing the inmate, that Edward is an expert manipulator who can "get inside your head". Edward is scheduled to be put to death by electrocution at 11:00 that night, and Dr. Martin is tasked with determining whether the killer is legally sane or if he is mentally ill and incompetent of the crimes he has committed. Moss hopes that Martin will disagree with Dr. Fischer who was ready to declare Edward insane. In their first discussion Edward inexplicably details various aspects of Dr. Martin's personal and professional life, and insists that he is a demon named Nefariamus who will answer to "Nefarious" inhabiting Edward's body. Nefarious states that he was able to
possess Edward as he was not
baptized and had committed sins in his childhood, such as stealing. He further details that, despite the doctor's initial assumption, he is not trying to escape punishment, and wants the body of his host to be executed. Nefarious tells Dr. Martin that before the day is over, he will also have committed three murders though the doctor states that this is impossible. Nefarious accuses Martin of
euthanizing his terminally-ill mother, as a means to acquire his inheritance from her. The doctor becomes defensive, stating that the decision was made after meticulous examination and angrily threatens to end their interview. Suspecting that Edward has
dissociative identity disorder with Nefarious being an
alter personality, Martin tries to speak directly with Edward, but only with limited success. Nefarious periodically allows his timid, beaten-down host to communicate as seen fit, while Dr. Martin then draws out the role of demons in the world through his discussions with Nefarious. Expressing his own personal beliefs as
atheistic, Martin declares that Edward has an insane belief system, and resolves to certify the prisoner to be unfit to be executed for the murders. As the doctor is leaving however, Nefarious begins to talk about the doctor's troubled relationship with his pregnant girlfriend and claims that at that very moment she is at an abortion clinic, mistakenly determined to rid the couple's relationship of what she sees as the reason he might leave her. The demon likens the practice of abortion to ancient
paganistic child sacrifices to
Molech, and in counting down gleefully exclaims "all hell is rejoicing". Dr. Martin rushes to call his girlfriend only to find that the abortion has already taken place. Upon returning to further evaluate Edward, the demonic personality continues to cause Dr. Martin to question his prognosis when the prisoner speaks in Latin. Nefarious tells the doctor, that he wants him to serve as the author of an already-written Satanic book titled
The Dark Gospel, and offers to give him everything he wants from his
master as was once offered to a
carpenter in biblical times (Jesus), who declined. Explaining that he has chosen Dr. Martin to bring forth this work to deceive and mislead all of
God's created human race, comparing the purpose of the book as the opposite of the
Gospel in the
New Testament. Nefarious claims to have known and been with Dr. Martin since he was a child. When the doctor is called away by Warden Moss, it is revealed that a scrapbook of Martin's life and the manuscript for
The Dark Gospel have been found in the prisoner's cell. Determining that the prisoner was intending to have Dr. Martin as his next victim, they confront Edward about what has been found. Nefarious causes the prisoner to dislocate digits on his hand, escaping his handcuffs and begins to strangle the doctor. Threatening to kill him unless he begs for his life, Martin concedes and tells him that he doesn't want to die. Releasing Dr. Martin, the prison guards forcefully apprehend the killer while Martin signs a document that declares Edward Wayne Brady as sane enough to be executed. In so doing, Nefarious declares that the doctor has committed three murders: his mother, his unborn child, and the prisoner. Leading to the execution, a terrified Edward begins to plead for his life and continues to state that the murders were not his own actions. In his final moments while sitting in the electric chair, Nefarious again takes control and asks Martin whether he accepts the offer that was made earlier in exchange for publishing the devil's gospel, to which Martin shakes his head "no". Edward suffers a painful and prolonged death by electrocution. The disembodied demonic Nefarious takes the chance to speak to the doctor stating that he should have taken the offer, before possessing Martin and forcing him to hold up a gun to those in attendance and then attempt suicide. Martin spontaneously asks God for help, and the gun he is using misfires. One year later, a visibly changed Martin is in a TV studio promoting a novel he wrote titled
A Nefarious Plot, explaining he has written it as a warning against the reality of the demonic forces tempting all of us. In the discussion during the interview, Dr. James Martin concedes that he experienced a
miracle as the firearm had been attempted three times while he was possessed and it did not work, as the gun when tested by forensics it functioned properly. Concluding that he is
agnostic in his approach to what happened, he expressed interest in learning more about
God and Christianity. Upon leaving the studio he encounters a homeless woman, who ominously addresses him by name and asks if Dr. Martin missed her — evidently now the possessed host of Nefarious. In a post-credits audio, the voice of Nefarious is heard to say in Aramaic and Latin, "You have been weighed in the balance and found wanting, but you are stupid that you do not understand. It is to be continued!" ==Cast==