The Ritual is a good old-fashioned slow-burner. It lets its characters do the talking, and when its subject matter is the ritual of exorcism, you'd reasonably expect the talking to fall on two sides of the equation of good and evil.

But anyone with shares in pea soup or Italian mopeds shouldn't get too excited. The Ritual is a purposefully domestic take on the subgenre, and it takes pains to tell us that it's based on real events. That opening title card could be taken as the first step in having a little faith…

It's the faith of well-liked but grieving parish priest, Joseph Steiger (Dan Stevens), that's rocked in The Ritual when he reluctantly takes an ill girl into his clergy house. He's convinced the symptoms displayed by Emma Schmidt (Abigail Cowen) can be explained by medical science. But Father Theophilus Riesinger (Al Pacino), an exorcist brought in to conduct the ritual, is convinced that Emma's only hope is performing the rites at that time and place. As the multiple rituals of exorcism unfold, priests and nuns alike find themselves affected while Emma's condition worsens.

The Ritual draws on a well-documented exorcism undertaken in late 1920s Iowa, most notably an account published in 1935 called Satan Begone! Sadly, the film didn't go with that title. Instead, as its name suggests, it sets its sights on solemnly breaking down the ritual along with its participants.

Ambiguity, often the key ingredient in exorcism films, is vital to The Ritual. It has mixed success balancing events with the reactions we see on-screen, but the script from Enrico Natale and director David Midell creates a swirling mix of apprehension and fear for characters to sink into during its lean 98-minute runtime. Fans of the exorcism subgenre will know many of the beats that come with that, but it plays refreshingly straight with its manifestations and crises of faith.

It helps that Midell employs techniques that are more usually seen in found footage or fly-on-the-wall documentaries. In and out of the rites, many events take place off camera, leaving us with long reaction shots before we are let in on the horror. The darting handheld camera and light crash zooms don't mask or create false scares, but help bring us closer to a selection of increasingly distressed characters. The ominous score of shrill and deep chords does the same.

Even better, with just a few exceptions to remind us this is a 1920s period piece, most of the film takes place in the walls of the rectory and convent. We live every night time creak and moan with the characters; an environment that, crucially, Emma is brought into. Among those characters are the priests determined to convince each other that they are right. Dan Stevens is robust as the unravelling priest, convincing with a mix of grief and pragmatism. Opposite him, Pacino exudes steely confidence. He doesn't phone it in, but he doesn't fully unleash either. In a measured performance, his hawkish eyes peer from a shock of hair and beard above a giant sack habit. Both performances are well matched, particularly during a key revelatory scene.

While this isn't for fans of the crash and wallop of demonic possession, it casts an effective net of dread and mistrust. But structuring the film into rituals—effectively chapters— makes it feel repetitive long before it rushes into its short third act and resolution.

The suggestion that forces are working behind the scenes—particularly “the enemy,” as Pacino's haggard Riesinger frequently calls it—is likely to be the one part that lingers after the credits. The Ritual is an earnest addition to the subgenre, then, but not one that breaks new ground or is likely to be remembered for its worthy adaptation of one of the most documented exorcisms of all time.

The Ritual is in cinemas from May 30th