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Creepy small-budget psychological horror flicks are a genre unto themselves at this point, with their fads pretty well established. So I figured I knew where Liam Gavin’s A Dark Song was going. But I was happily surprised.

The film opens on Sophia Howard (Catherine Walker), a reserved and intense woman, renting out a large abandoned house in the Welsh countryside. She heads into town and has a meal with Joseph Solomon (Steve Oram), a bald and bearded oddball with a fierce sense of his own importance.

Through snippets of terse dialogue, it becomes clear that Joseph is part of a small circle of experts in the occult, and Sophia has asked him to carry out some kind of ritual. Several years ago her son died, and she wants to speak to him again. This will require summoning up an angel, but breaking the barrier between worlds risks attracting darker demonic forces as well.

Gavin’s script is sparse on dialogue, save for a few portent-heavy speeches. Sophia and Joseph construct elaborate occult designs on the floors of various rooms, each to serve a particular spiritual purpose. Under Joseph’s instruction, Sophia fasts for days, sits in key places for just as long; sometimes she’s soaked and shivering. She goes vast stretches without sleep, concocts diaries of elaborate symbols, sometimes has to drink blood.

In many ways, A Dark Song is an endurance film, and Gavin draws unnerving dread out of its grueling physicality. His camera relies on long takes to observe silences and preparation, painting the house interior with grim earth tones. Certain shots create tension by splitting the screen in odd ways, or leave empty frame space that looms over the characters, threatening to be filled with… something. The Welsh landscape is bleak, greenish fields under steel-gray skies. The score, by Ray Harman, is more a mix of eerie pulsing drums, scratches, and basso strings. The overall result is an unsettling mood poem, albeit one that’s more visceral than deep for most of its running time.

Other than the rental agent (Mark Huberman), and a chance encounter Sophia has with her sister (Susan Loughnane) while stocking up on supplies, Sophia and Joseph are the only two (human) characters in the film. The ritual takes months and permits neither character to leave the house for its duration. So the vast majority of A Dark Song takes place within that space, lending it a feverish slow-burn sense of ever-deepening unreality. As the weeks drag on, Sophia becomes thinner and more hollow-eyed. Doors open for no apparent reason, some of her son’s toys showing up in random spots, and she glimpses figures in the shadows. Is occult magic even real? Is Joseph merely using her? Are they both losing their minds to a twisted fantasy?

Joseph himself is a study in weird contrasts. Sophia considers him an expert, and we invest him with authority out of respect for her. But half the time he comes off as an overgrown “Dungeons and Dragons” fan. He rockets between laid-back confidence, outraged fury, profound self-centeredness, and an almost childlike loyalty to Sophia and her quest.

The encounter between Sophia and her sister clarifies the depth of her rage at God. That she may be violating the moral order or even endangering her soul does not give her the slightest pause. Walker’s performance invests us in her character’s quest for cosmic justice, and gives Sophia steely focus. But the character’s boiling fury goes even deeper than we realize. The story of her son’s death is more complicated, and her reasons for the ritual far darker, than she initially lets on. “I don’t do forgiveness,” she snarls at Joseph at one point.

When he realizes the truth, Joseph is thrown into a genuine panic. His terror at what Sophia’s lies could mean for the stability of the ritual and for the fate of both their souls heightens the stakes. Joseph must improvise the ritual from then on, taking them both into grimmer territory.

For a while, A Dark Song feels like a better version of other films, seemingly following the path of stylish nihilism they’ve trod before it. But ultimately, the grueling ordeal opens up layers of humanity in both Sophia and Joseph that we don’t expect. The questions raised by Sophia’s purpose reveal new thematic depths in the final act. For its final revelation, A Dark Song swings for the fences visually, or at least as much as such a film can on a limited budget. A lesser director would lose control of the tone, but Gavin’s purposes carry us through.

He has things on his mind beyond nihilistic stimulation. The brutality of the film has a point. And for that, I was grateful.