Of course, the primary precursor of The Ninth Configuration is Blatty's own Twinkle, Twinkle, "Killer" Kane. While The Ninth Configuration is a tighter book than Twinkle, Twinkle, "Killer" Kane, with a better mystery setup and a stronger thematic focus, they share basic concerns, characters, and themes. The earlier book is in some ways funnier, with even more pop culture play (a dog dropping on a bed is labeled "Brand X") and even more zaniness by the inmates. Moreover, many subplots were trimmed in the rewrite, ranging from minor—a very funny revolt by a computer, presaging the computer error that sends Kane off as a psychiatrist—to more major.

One major subplot concerns The Consuelo Endicott College for Girls, next door to the castle housing the military mental cases; characters from the college, including Miss Mawr, Clydene Sloop, and the Founder, provide further color...