Norwegian writer-director Camilla Strøm Henriksen’s impressive debut is an intelligent family drama refrigerated with horror-movie chills. Partly autobiographical, it’s the story of teenage carer Jill (Ylva Bjørkaas Thedin), who looks after her little brother and their depressed single mum. This is a family unlikely to show up on the radar of social services: Jill’s mum has had some success in the past as an artist; her dad is a famous jazz musician and rarely around.

The claustrophobic first half, with echoes of Polanski’s Repulsion, is confined almost entirely to Jill’s flat where mum Astrid (Maria Bonnevie) swings between depressive slumps and manic bursts of creativity. There’s psychological depth and rawness to these scenes that’s painful to watch. Feeling she’s a failure as an artist, Astrid moans about the meaningless of life. What about us, your kids, Jill asks. “It’s not enough.”

Cleverly, Henriksen locates the terror inside the home – Jill’s daily dread of walking in after school into some scene of unspeakable awfulness. Her fear is externalised into imaginary rodents that scuttle across the floor.

The second half turns more formulaic as Astrid’s mental health worsens and Jill pins her hopes on a visit from her dad, in town for a gig. He turns out to be a pampered narcissist. “You’re my toughest critics,” he jokes to Jill and her brother; he can’t deal with their emotional demands.

After the intensity of the first half, it feels a bit hollow and underwhelming. I found the seductively Scandinavian Instagrammable interiors and freakishly good-looking blond leads increasingly distracting.

• Phoenix is released in the UK on 13 September.