Along with a lot of the film movements from the 70s that were dismissed as trash at the time, slashers have enjoyed their reassessment by cineastes and are now big business in Hollywood, a lot of these old films barely even mentioned by the critical firmament now recognised as classics.

Black Christmas is one of them, held up as one of the prototypes of the slasher genre alongside better known examples like Halloween or Friday the Thirteenth.

What I found most interesting about it however was that even though it contains a lot of the tropes that made the slasher movement what it was – the sorority house full of pretty young women, the final girl archetype, the POV of the killer with his heavy breathing on the soundtrack – I didn't consider this s slasher.

It wasn't scary, there was no blood, and you don't see any iconic and distinctive killer – the elements that made slasher villains as venerated as Darth Vader or Godzilla. It was just a murder mystery that happened to take place in a classic slasher movie setting.

So without all the juicy elements that would bring the genre to life later like the gore, the jump scares and the murder-as-punishment-for-sex motif, all it has to go on is to be an effective murder mystery.

The girls of the sorority are mostly well behaved, apart from the hard-drinking Barb (Margot Kidder), but when the killer (in POV shots) climbs the wall and enters the attic space, you know their days are numbered.

For weeks they've been getting obscene phone calls that have been rattling the more pure-hearted members of the house like Jess (Olivia Hussey), but when Barb answers she has a great time taunting the creep back.

But after one of their number disappears after going upstairs to pack for a forthcoming trip, nobody worries too much, assuming she's snuck out to go to a party. Even the matronly house mother Mrs MacHenry is more concerned with the many hiding places her booze is stashed than anything else.

But the missing girl's father comes around because she never showed up to meet him, and along with some of the more level headed of the girls, goes to the police to report her missing.

There they learn another local girl has vanished too, so they agree to help the cops search the local park, and at the same time Jess is having an argument with her boyfriend Peter (Keir Dullea, of 2001 fame) over her plan to abort the baby they've conceived together.

Bodies start to pile up (although still with no blood on screen) when they find the young local girl's corpse and the drunk house mother comes across the missing student's body and is quickly dispatched by the killer too.

Finally the wiretap the cops have put on the phone leads to one of the most iconic moments in horror – one so popular at the time (and based on a true case) it was repeated in 1979's When a Stranger Calls.

The script by Roy Moore goes a bit off the rails towards the end, tying itself in a so many knots to keep you guessing it loses most of the impact it's going for, and while Black Christmas isn't the best horror movie and not even the bloodiest or scariest slasher (if that's what it is), you need to see it to understand where an entire subgenre of movies that flourished in the 70s and 80s came from.