Set in a few rooms of a shared house, the technical scope and thrills director Ian Tuason provides in his feature-length debut are admirable and enjoyable. The story follows a paranormal podcaster, Evy (Nina Kiri), who lives with and cares for her bedridden, comatose mother (Michèle Duquet). Evy and her co-host, Justin (Adam DiMarco)—who records remotely and remains offscreen for the duration of the film—unravel a slate of ten cryptic audio files received via email. The files feature a woman uttering bizarre sleep-speech that, when played backward, unearths creepy mysteries.

On the podcast, Evy plays the skeptic to Justin’s believer. Her setup is positioned at a dining room table facing a wall; with her computer, mic, and noise-canceling headphones on, her back is turned to the open doorways behind her. Only the skeptical or unafraid would sit this way—unbothered that demons could be lurking behind them in the doorways! But even Evy begins to get rattled by the recordings. She starts having nightmares and is shaken by odd occurrences around the house, such as flickering lights, strange noises, running faucets, and ghostly visions. Kiri’s performance is subdued, with small tics signaling her eventual unraveling.

A somewhat spare film visually and narratively, undertone primarily runs on its masterful sonic design. I viewed the film in a theater with Dolby Sound, where ghostly voices bellowed around me and every bump in the night reverberated through my headrest. (I’ve always wondered what Sensurround felt like in the 1974 film Earthquake, and perhaps this comes close.) The immersive effect of the sound work and its varying volume levels—from the calls between the podcasters and the eerie breathing of Evy’s mother to loud, mysterious thumping—is why the film is consistently effective, even if the storyline is somewhat lacking. (Tuason is set to direct the next entry in the “Paranormal Activity” saga, which should highlight his talents and perhaps revive the series.)

There’s a DIY feeling to the film and its humble podcasters that recalls the ghost hunters of the similarly minimalistic The Blair Witch Project (figures with turned backs appear here too). Catholic paraphernalia adorns the walls with a sense of unease: A small, white Blessed Mother statue with a haunted, open-mouthed expression appears in one place, only to be found elsewhere as if it moved on its own. This imagery, along with the low-lit rooms shot from foreboding angles and a pale, green-carpeted spiral staircase, is reminiscent of The Exorcist. (According to the press notes, the movie was actually shot in Tuason’s childhood home in Toronto.) The cinematography by Graham Beasley, also working on his first feature, employs many unnerving close-ups, including the waveforms of the audio files.

The repetitive day-to-night structure over the course of a few days doesn’t quite deliver the goods, leading up to the tenth audio file. While I was enraptured during the screening, the film didn’t linger afterward, perhaps because the conclusion feels muddled. Still, undertone is a kicky horror romp that shows promise for Tuason and his creative team—one that should jolt even those discourteous patrons into putting away their phones.