"Common sense breaks down at subatomic level" says a theoretical physics professor early on in John Carpenter's Prince of Darkness, and so it does, as a group of students and scientists gather in the basement of an abandoned church to study an impenetrable container covered in satanic inscriptions, filled with a bizarre green liquid. They run numerous tests, and the results are unexplainable: the acidity can't be that high; a life form can't grow in pre-biotic fluid; how can it be seven million years old? As baffling as it seems, these scientists, who value their fields of study more than their names, still reject the idea that this is real, even as the mounting evidence becomes harder and harder to dismiss.
Carpenter, as with much of his work, thrives in tight spaces, drawing horror from pitch-black rooms, long narrow corridors, and the imposing presence of scientific apparatus and religious iconography cluttering the already cramped church; while his use of nauseating practical effects catalyses his characters' acceptance of the situation - after all, who can deny the occult when a person collapses into a pile of cockroaches? It's at this point that Carpenter shifts gears. The mystery of the green liquid suddenly reveals itself, and the earlier scepticism is replaced by a panic-stricken fight for survival: one of the students tries in vain to reason with his possessed captors by telling (terrible) jokes, while another, seeing the hordes of zombified people blocking the alley beneath the first floor window, jumps down anyway to look for an escape route, before frantically climbing back up as the crowd closes in.
Perhaps the most important reaction, though, is between physics students Brian and Catherine, the two "leads", or at least the two characters Carpenter spends the most time with. Early in the film, they're involved in a string of non-committal sexual encounters on campus, yet when faced with the devil incarnate, they profess their love for each other, as if the irrational situation they're in has made them more prepared to accept the unbelievable. It's fitting, then, that this film about scientific investigation ends with an act of romantic optimism - which Carpenter preserves with a gorgeous cut to black.