In the second half, the film becomes darker as it delves deeper into its central issues of human suffering, sacrifice and faith.

In the early 1970s, towards the end of the Vietnam War, a castle in the Pacific Northwest is used by the US government as an insane asylum for military personnel.

Among the patients there is former astronaut Billy Cutshaw, who aborted a Moon launch and was dragged screaming from the capsule, suffering from an apparent mental breakdown.

Lieutenant Reno, who is there attempting to stage Shakespeare plays with a cast of dogs, suspects that Kane is crazy himself.

Realizing Kane's mental state, the Army psychiatric staff maintained the charade and sent him to Fell's hospital under the pretext of being its commanding officer.

Rushing back in, Cutshaw discovers that Kane had actually been injured in the bar fight and refused to get help, effectively committing suicide to provide proof of human goodness.

So I rewrote it and fleshed it out, Cutshaw became the astronaut in The Exorcist that Regan warns about going into outer space and fully developed the deeper implications and theological themes.

[5]However, Blatty subsequently stated he preferred the first version of the book to the second: "...the first one is infinitely funnier and wilder, and stranger and more of a one of a kind; the second one has the same plot, but the prose is more finely crafted, I think.

[7] Ironically, Warner Bros. wound up initially releasing the film in selected markets, despite Blatty's misgivings.

Blatty retained Jason Miller, who had played Father Karras in The Exorcist, for The Ninth Configuration.

For the central role of Colonel Kane, Blatty cast Stacy Keach (another contender for the part of Father Karras in The Exorcist).

Blatty had originally cast Nicol Williamson in the role of Kane, before deciding that the British actor was wrong for the part: "I was deluding myself.

"[8] Stacy Keach recalls the situation differently: "Ironically, I was the lucky benefactor of a Nicol tantrum in the late '70s.

William Peter Blatty wrote and directed it and financed part of it by selling a home that he had in Malibu.

His idea of getting a good ensemble effort from his actors was to take people over to Budapest for two months—the part I had might have taken two weeks in the States but he had us all over there for two months.

"[10] Blatty himself appears briefly near the start of the film as a patient pretending to be an army doctor (he is the one who stole Ed Flanders' pants; the role was originally intended for George DiCenzo, but once Michael Moriarty dropped out, DiCenzo was given the role of Fairbanks, originally intended for Scott Wilson, and Blatty decided to fill the role himself), and would later cast Jason Miller, Ed Flanders, Scott Wilson, and Nicol Williamson in his next film as writer/director, The Exorcist III (1990).

United Film Distribution (UFD), affiliated with the United Artists theatre chain and best known for releasing George A. Romero's Dawn of the Dead, picked up the film for a planned December 1979 release; however, the company dropped the picture, and Warner Bros. subsequently picked it up.

[11] It was not a commercial success upon its cinematic release in 1980; however, it received generally strong reviews and a Best Picture nomination at the 38th Golden Globe Awards in January 1981.

Blatty re-edited the film for its 1985 re-release, which was distributed by New World Pictures under the original title, The Ninth Configuration.

Leonard Maltin has described the movie as "hilarious yet thought-provoking, with endlessly quotable dialogue and an amazing barroom fight scene.

Kermode has described The Ninth Configuration as "a breathtaking cocktail of philosophy, eye-popping visuals, jaw-dropping pretentiousness, rib-tickling humour and heart-stopping action.

From exotically hallucinogenic visions of a lunar crucifixion to the claustrophobic realism of a bar-room brawl, via such twisted vignettes as Robert Loggia karaoking to Al Jolson and Moses Gunn in Superman drag, Blatty directs like a man with no understanding of, or interest in, the supposed limits of mainstream movie-making.

The result is a work of matchless madness which divides audiences as spectacularly as the waves of the Red Sea, a cult classic that continues to provoke either apostolic devotion or baffled dismissal 20 years on.

In some versions released during the intervening years, an alternate ending was used in which it is said (via added voiceover by Stacy Keach) that Kane died of wounds inflicted by the bikers.