Audiences were shocked by The Exorcist in 1973, probably because it involved a 12-year-old girl, Regan (Linda Blair), being possessed by a demon, swearing like a docker, vomiting fountains of green goo, and stabbing herself with a crucifix. But William Friedkin's film wasn't just a shocking horror movie, it was a box-office smash which was nominated for 10 Oscars, including best picture; William Peter Blatty went on to win the best adapted screenplay prize for a script based on his bestselling novel.

It was always going to be impossible to recreate such a phenomenal success, but that hasn't stopped people trying. There have been several forgettable Exorcist sequels and prequels already, and now, to mark the original film's 50th anniversary, David Gordon Green has made a follow-up that is intended as the first part of a trilogy. From 2018 to 2022, he directed three Halloween films starring Jamie Lee Curtis, so making legacy sequels to 1970s horror classics is obviously his favourite occupation.

The Exorcist: Believer has a similar scenario to The Exorcist, only this time the girl is Angela (Lidya Jewett), and the single parent is Victor (Leslie Odom Jr), a widowed photographer. Victor is a loving father, if a little over-protective: he doesn't even want his daughter to study with her friend Katherine (Linda Blair-lookalike Olivia Marcum) after school. Still, perhaps he has a point, because Angela and Katherine sneak off into the woods to see if they can contact Angela's late mother via a seance. They aren't seen again for three days, and when the girls are eventually found on a distant farm, they have no memory of what they've done or where they've been.

You can guess what happens next. Both girls start attacking people and swearing in croaky voices, which means that it won't be long until all the other time-honoured symptoms of demonic possession appear. The atheistic Victor and Katherine's deeply Christian parents try to work out what's going on. Could the girls have been assaulted? Could puberty have brought on some kind of psychosis? Could they have visited a nearby homeless people's camp?

As long as these questions are in the air, The Exorcist: Believer is an atmospheric, quietly unnerving, meticulously constructed supernatural mystery. Maybe it indulges in too many references to the first Exorcist: just because Father Damien (Jason Miller) hit a punchbag in a boxing gym in 1973, there is no reason to have Victor hitting a punchbag in a boxing gym 50 years later. But in general Green and his co-writers do a clever job of evoking the original film's autumnal feel and credible characters, while establishing a new setting and new themes that are intriguing in their own right. The idea of two girls being possessed simultaneously is a promising one, too. Until about halfway through, I was a firm believer in The Exorcist: Believer.