THE effect of divorce and subsequent custody battles has been a frequently explored subject in cinema over the years, from Kramer vs Kramer to this year’s Loveless and beyond.

It’s endlessly impressive, then, that French director Xavier Legrand’s debut feature film (an expanded continuation of his Oscar-nominated short film Just Before Losing Everything) provides a genuinely enthralling portrait of that insidious family bitterness that steadily escalates tension to a powerful crescendo. It’s not hard to see why it was chosen for the coveted audience award at this year’s Glasgow Film Festival.

Miriam (Léa Drucker) and Antoine (Denis Ménochet) are a long-time married couple whose relationship has broken down beyond the point of repair, leading them into a bitter divorce and subsequent vicious fight for custody of their embattled 12-year-old son Julien (Thomas Gioria).

They also have a daughter, the much older Joséphine (Mathilde Auneveux), who is more emotionally equipped to deal with what’s happening and to physically escape her father’s abusive shadow in particular.

But what about Julien? One of the film’s most astute dramatic avenues is to examine what effect all this has on a boy at such an impressionable age, caught in a situation beyond his control yet one that devours his every waking minute.

In a deeply impressive debut performance by Gioria, we really feel this little boy’s pain as he is clearly better off with his fraught but still caring mother, affectingly played by Drucker, while being forced to spend court-allotted weekend time with his overbearing, often downright scary father.

As a piece of drama it provides a fascinating look from the younger child’s perspective, uncomfortable and often frightened in his father’s company. Scenes of the two of them in the car, his father grilling his son for information on his mum’s new boyfriend as Julien visibly shakes, are a tough slice of realist drama to behold. But he is still his father at the end of the day, right? The film deftly digs into what that means when bad behaviour becomes an unavoidable factor.

Antoine is wonderfully played with a captivating mix of icy distance, self-righteousness and ticking time-bomb volatility by Ménochet (many may recognise him as the French farmer at the beginning of Quentin Tarantino’s Inglourious Basterds).

The depiction of the strained father-son relationship will hit uncomfortably close to home for anyone who grew up with more stern patriarchal looks than warm hugs.

When the case is being heard in court, we’re put in the judge’s shoes of choosing to believe Miriam’s stories of Antoine’s domestic abuse or give him the benefit of the doubt. Legrand’s shrewd filmmaking trick is to chip away with a measured, slow-building tension at the idea of there being two fair sides of this story, with Antoine’s abusive true self unveiled the more he sees the perceived injustice of his wife moving on without him.

Without need for showy camera moves or easy answers to his complex questions, Legrand has sculpted a fastidious family drama with a social realist power, one with a strong emotional beating heart, an uncompromising way of unveiling its characters’ flaws and a deafening ring of truth about it right up until its almost unbearably tense ending.