A killer in black motorcycle garb is murdering women in Boston, depositing the heads of his victims in whatever water is closest at hand. Police lieutenant Austin's (Leonard Mann) investigation leads him to a girl school where several of the victims were students. The cop's suspicions quickly concentrate on anthropologist professor and jerk Vincent Millett (Drew Snyder), who does not seem to have student he hasn't slept with (must be the hot anthropologist sex into which we will be given unwanted insight by the movie, because it sure as hell can't be his looks).
When he's not sleeping with his students, Millett lives with his research assistant and lover Eleanor (Rachel Ward), with whom he shares a deep interest in the headhunters of Papua New Guinea. Oh, and all of the victims had something to do with Millett. Despite everything about the case being pretty damn obvious, it'll take quite a few dead bodies, and heads in sinks and toilets until it can be closed.
In 1981, the slasher movie genre wasn't quite as codified as in the years to follow, so it was still possible for a movie to (sort of) belong to it without being about a bunch of teenagers getting slaughtered in the woods or a dilapidated building. Ken Hughes's Night School differs from many other slashers by trying to incorporate elements of an actual mystery, where the killer's identity stands in question. Even red herrings make an appearance. I assume a more direct influence of the giallo than usual. This theory is compounded by the styling of the killer with its shade of Strip Nude For Your Killer, some very typical shots of spiral staircases, and the rather bizarre way the mystery is set up.
This may sound like quite an exciting combination, for what's better than a slasher that comes to the genre from a different direction, but the killer's identity is so obvious, and the whole investigative aspect so undercooked, it's difficult for me to conjure up much enthusiasm.
It doesn't help Night School how unbalanced a film it is. Tonally, it jumps from neatly done stalk and slash sequences, to bad melodramatic acting, to tasteless and overlong suspense scenes based on the question "where will they find the head this time?", to boring police procedural, to unfunny humour and back again, without ever reaching the point where these elements come together in entertaining, interesting, or dream-like ways. It's as if Hughes couldn't (or wasn't allowed to) decide what type of horror film he was trying to make and so ended up trying to make all of them at once; this seldom ends well for a movie or its audience.