I wonder if this was greenlit because of the success of Sydney Sweeney exploitation jam Immaculate. That film did such a fantastic job of evoking the plots, design moods and aesthetic of the era that gave us classic religious horror flicks like The Exorcist, The Omen and Rosemary's Baby that this effort feels like an also-ran, even despite being ostensibly part of one of those franchises.

If you haven't seen Immaculate you might get more out of this movie – it's written, directed and acted with perfect adequacy and not much more. The standout moment is Charles Dance as an elderly priest and what befalls him (literally) with a pole from a collapsing scaffold, but it even tries to homage the nanny hanging scene from the 1980 original without much finesse.

American nun Margaret (Nell Tiger Free) arrives in Rome to take her vows and accept her place at an orphanage in the mid 70s in a time of political unrest, with protesters filling the streets and the social mood threatening to explode.

Despite her surroundings, everyone seems friendly including her fellow novice roommate and most of the senior nuns. The one dark spot is the young orphan Carlita, who doesn't speak, seems to be constantly locked in her room and creates disturbing drawings of horrific visions she apparently has.

As Margaret plunges deeper into the mystery at the centre of the convent, she's approached by the priest we met in the beginning, Brennan (Ralph Ineson, who needs to watch out for typecasting), who's now disgraced but tries to warn Margaret of the great danger coming and explains the entire plot (which I won't spoil here but again – if you've seen Immaculate, you've seen the same idea done better).

Margaret doesn't want to hear about institutional conspiracies and the coming of a great evil, she just wants to know what's going on in the shadowy corners of the orphanage and help Carlita, who she believes is a victim of abuse rather than a danger.

She discovers a hidden vault underneath the office of the Abbess, and (no surprise), what she discovers sends her back to Brennan when she realises he wasn't crazy after all. Of course, Margaret is going to discover she has a more personal part to play in the story than she imagined, and it all ends in a bloody fugue state with the senior members of the church standing around in a darkened chamber full of candles in dark robes like you know it will.

You'll feel a frisson of pleasure when the final scene ties the film to the rest of the franchise as Brennan reveals what's happened to the baby (and his name) that's pivotal to the plot, but even though everything's staged, acted and directed well, it's referencing far more than it's creating on its own.