I don’t think I’ve seen a better movie about domestic abuse than Xavier Legrand’s taut thriller, “Custody.” It’s brutal in content and equally brutal to watch. But it gets to you in unexpected ways in capturing the fear of just being in the presence of a human time bomb capable of detonating at the slightest provocation.

Legrand, in continuing the story begun in his 2013 Oscar-nominated short “Just Before Losing Everything,” gets almost everything right in his first attempt as a feature filmmaker. That includes the casting of pint-sized Thomas Gioria as Julien, the 11-year-old pawn in a borderline insane father’s relentless game of stalking the child’s terrified mother. The boy needn’t speak a word because his body language, especially his expressive eyes, is the very definition of anxiousness.

At first, you think Julien is overreacting to his father’s gruff demeanor during one of his court-mandated weekend visits. Then, as the bearded, barrel-bodied dad commences interrogating the kid in a depraved search for information about his mother’s whereabouts and living situation, you can sense the panic. And it’s frightfully clear this isn’t the first time the child has feared for his mother’s life — or his own. How could it possibly get worse? That it does is all due to Legrand’s laudable knack for continuously raising the stakes while ratcheting up the tension. It’s a gift he liberally exploits to the point you literally can’t stand to bear another moment of the suspense.

To think it all started off so banal, with a hearing in family court, where a judge is hearing arguments as to why Julien’s pretty-but-frail mother, Miriam (Léa Drucker), should share her son with an ex-husband in Denis Ménochet’s intimidatingly brutish, Antoine, who she can’t seem to escape — even after moving hundreds of kilometers away, only to discover he’s quit his job and relocated to the same town. The judge (Saadia Bentaieb) is a bastion of impartiality, at one point noting she’s unable to tell “which of you is the biggest liar.”

It’s all very neat and legal, and it’s clear Legrand thinks it’s so politically correct that it just might get people killed. And there lays the premise for his absorbing film, as Legrand petrifyingly illustrates how the law and human nature don’t necessarily see eye to eye. At the courthouse, Antoine may seem calm and genuine, telling the judge he just wants to share in Julien’s life. But out in the wild, he’s a badgering bully in his passive-aggressive attempts to pump information from Julien, who sits cowering in the front seat of Antoine’s small, claustrophobic van.

There are three or four such scenes, and you marvel at how real these moral confrontations project. It’s as if Legrand has been in the very same position, possibly when he was a child star (appearing in Louis Malle’s “Au Revoir Les Enfants”), and cast as his parents reluctant go-between. Even if that’s not the case, you sense it is because these moments are so genuinely unnerving. Unlike his mother and soon-to-be 18-year-old sister, Josephine (Mathilde Auneveux), Julien has nowhere to hide or retreat. He’s ordered by law to spend time with Antoine whether he likes it or not.

It’s a no-win dilemma that draws long and deep on your empathy, at least when you’re not cursing a legal system that puts young kids in such a potentially dangerous situation. And where is the protection for Julien’s mom, who lives in constant fear of her insanely jealous ex? If there’s a better way, Legrand offers no answers. What he does do, is give us a glimpse at Antoine’s inept excuse for parents, a look that shows the proverbial apple doesn’t fall too far from the tree in a perpetual chain of spousal abuse. Bullies indeed breed bullies. And in “Custody,” it’s a problem that could well end tragically.

“Custody”
Cast includes Léa Drucker, Denis Ménochet, Thomas Gioria and Mathilde Auneveux. (In French with English subtitles.)
(Unrated)
Grade: B+