For the second time this year, a powerful new film addresses the fall-out from a toxic marriage for its children. In February’s Loveless, an unwanted son disappears. In the French drama Custody, a boy is caught in the middle of a parental trap that may well end in violence.

Like Loveless, this is an exceptional, powerful piece of work; though its impact on our emotions is through different tools. Here, writer-director Xavier Legrand blends social realism with tropes from thriller and even horror films, to evoke the daily tension, fear and emotional confusion that result from domestic violence.

It starts with controlled calm, as a separated couple, Miriam and Antoine Besson (Léa Drucker and Denis Ménochet) and their lawyers sit before a female judge to discuss custody rights. Their daughter Joséphine (Mathilde Auneveux) is nearly 18 and doesn’t enter their discussion. The issue is 11-year-old Julien (Thomas Gioria).

The boy has written a statement himself, which the judge reads aloud, in which he speaks of violence and fear and his desire not to see his father. Not surprisingly, the adults have different stories to each other, and body language to match: Miriam seems aggressively uptight, Antoine softly reasonable, the wronged husband who just wants to see his children. The judge rules for joint custody.

There is such a verité, procedural air to this scene that one might anticipate a dry film about the court system’s handling of family cases. On the contrary, it’s the calm before the storm.

A few years ago Legrand made an Oscar-nominated short film that introduced this family and its problems. Anyone who saw that will know from the outset where this is going to lead; if you’re new to the Bessons, it doesn’t take long to see Antoine’s amenable façade drop away.

It’s poor Julien who bears the brunt of it, caught in the middle as the intense Antoine uses his allotted time with his son to vent grievances and grill the boy for information about his mother and, in particular, the location of their new home – Miriam sensibly using her parents’ house as a decoy.

The scenes between father and son are almost impossible to watch. Thomas Gioria has an angelic, extremely expressive face – he doesn’t need words to convey a well of emotions, among them anxiety and a young boy’s determination to protect his mother. Ménochet has eyes like De Niro’s – smiling, until they go dead – and a bulky build that he uses to create maximum intimidation. The actor doesn’t spare his young co-star as Antoine’s tactics become increasingly fearsome. In the background, Drucker is also excellent as the long-suffering, tightly-coiled Miriam.

Legrand is laying out the mechanics of domestic abuse: a woman constantly on high alert, in the knowledge that the wrong word or gesture can flip a violent switch in the man before her; a psychotic unable to understand why he can’t simply remain with the wife and kids he thinks he loves; the children demonstrating different emotional effects of an adversarial childhood; grandparents looking on with dismay.

There’s a welcome absence of soundtrack to the film, Legrand leaving the emotional heavy lifting to the performers. This also allows for the phenomenal impact of Joséphine sweetly performing a song at her 18th birthday party, while her mother and others attempt to deal with Antoine outside.

Eventually the slow-build reaches a white-knuckle climax. Here, as throughout, Legrand exercises impeccable judgement, neither losing his grip on the tension nor ruining it all with a wrong call. The result is an auspicious first feature, as nerve wracking as it is, sadly, all too true.