If you loved The Ninth Configuration, try The Exorcist III
A bridge between a film you've already seen and one most people haven't. Here's what they share, and what the second one does that the first one doesn't.
What they share
Both films are directed by William Peter Blatty, and they sit in Horror / Mystery territory. If that's the register that drew you to The Ninth Configuration, the second film will land in a comparable space — through a different lens.
What The Exorcist III is
Georgetown, autumn—cold rain on a crucifix carved from bone. A detective pieces together a killer copying blasphemies from twenty years past. The devil’s footnote hums in chiaroscuro.

