“Families are the scariest thing on the planet,” says a teenage girl in this Irish horror film from young director Kate Dolan, making a seriously impressive debut. It’s the dead of night in a suburban cul-de-sac outside Dublin: a baby is in the middle of the street, alone and whimpering in its pushchair. A woman scurries out of a house, pushes the buggy into nearby woods and lights a fire.

For the next hour or so the film feels like a slow-burn slice of drab family drama: claustrophobic, but not obviously supernatural. The unsettling sound design begins to reveal the truth; all clanking pipes and whistling winds. Hazel Doupe is terrific as quiet, introspective teenager Char, who lives with her mum Angela (Carolyn Bracken) and granny Rita (Ingrid Craigie). Their semi is decorated in the late-70s style you only now ever see in horror movies: everything in shades of brown, including a velvet sofa the colour of overbrewed tea.

The scene with the baby is one of Char’s recurring dreams. Mum Angela spends most of her time in bed, medicated to blankness; she has “low days”, is how the family puts it. Something is clearly wrong – but who or what is poisoning their home? Perhaps it’s Rita, a dabbler in Irish folkore. (She looks the part of creepy horror-movie older woman, beady-eyed and a bit batty.) Or maybe its Char’s uncle Aaron (Paul Reid), who seems tense, possibly controlling.

After mum Angela disappears for a few days, she returns bright and upbeat – unnervingly so. Then horrible things start to happen. Though the film ends with a pretty standard-issue horror climax, Dolan pulls off some terrifying moments using pleasingly lo-fi techniques: something revealed in a mirror that made me yelp; the sickening snap of a bone breaking; a limb twisted grotesquely. And intense performances by Doupe and Bracken give it a real emotional pulse.

• You Are Not My Mother is released on 4 March in Ireland, and on 8 April in the UK.