It stars Jordan Belfi as a psychiatrist who must determine if a convicted death row inmate (Sean Patrick Flanery) is faking his alleged demonic possession.

[3] 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.

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.

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.

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.

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.

[7][8] The movie completed its box office run by earning $5.4 million from the 933 theaters it screened, before finding notable success streaming, digital and home media platforms.

[7] Bill Goodykoontz of The Arizona Republic gave the film two stars of a possible five, stating that it lacked subtlety and that the expressed views of the demon were simply a mouthpiece for the filmmakers.

"[13] Michael John Petty of Collider favorably compared the movie and its source material, to the 1998 film Fallen, The Conjuring series, and to a greater extent The Screwtape Letters by C. S. Lewis, and states that "Nefarious rises above the general clichés associated with faith-based productions and stands out as something increasingly more interesting than its religious contemporaries.

Confirming that Sean Patrick Flannery and Jordan Belfi are both scheduled to reprise their roles, the author stated that negotiations with distributing networks is ongoing.