If some viewers found “Barbie” too anodyne even for a comedy, then the return of France’s “bad-girl” director, Catherine Breillat, should give them something more substantial to grapple with as she interrogates patriarchy and sexual politics. Known for provocative films such as “Fat Girl” and “Romance,” among others, Ms. Breillat adds to her controversial yet trenchant streak with her new movie “Last Summer,” focusing as it does on a relationship between a middle-aged woman and her teenage step-son.

The film opens with an intense scene, as protagonist Anne, a lawyer, interviews a client about her claim of rape. Anne makes it clear to the young woman that the defense will be merciless in its interrogation of her sexual behavior. Right from the start, through harrowing subject matter and steadfast, merciless closeups, we’re back in Ms. Breillat’s particular world of expressionistic realism.

We’re soon introduced to Anne’s husband Pierre and their two small, adopted daughters. The family live in a gorgeous home situated in what looks to be the countryside. Anne and Pierre appear to be in a loving if passionless marriage, with complaints arising more from talk of taxes and government bureaucracy than from any interpersonal problems. This idyll is soon tested, though, when Pierre’s teenage son Théo, who was living with his mother in Geneva, comes to stay after apparently assaulting a teacher. 

Théo is played by Samuel Kircher, son of actress Irène Jacob, and with his cherubic face and long, blondish locks, Ms. Breillat is patently making a reference to Björn Andrésen, who portrayed Tadzio in the Visconti’s “Death in Venice,” a similar tale of adult infatuation with adolescence. As Anne and the young man become acquainted, the director builds their sexual tension carefully, with scene after scene detailing their growing physical intimacy — one that veers from normal mother-son tenderness. 

While on an outing to a local lake, Ms. Breillat pinpoints when Théo’s interest in his stepmother turns to thoughts of sex, particularly when Anne forcefully dunks him underwater. On the drive back home, with Sonic Youth playing on the soundtrack, he not only realizes that Anne is a force to be reckoned with but begins to fancy her.

It’s difficult to determine when Anne falls for Théo. Maybe it starts when the two talk of tattoos, when he teases her about secretly wanting one herself and even gives her a crude, simple one in her cubital fossa, which he also caresses and kisses. Actress Léa Drucker convincingly portrays Anne’s bemused incredulousness in response to his attentions, and she plays off the forearm kiss with a smile, but it’s clear — with each line Théo crosses and she allows — that the character is succumbing to desire. 

Later, while Pierre is away on business, naturalment, a kiss on the mouth occurs, and it’s certifiably French in its intimacy. Known for her frank sex scenes, Ms. Breillat crafts a few for “Last Summer,” though they’re hardly in her trademark explicit style. What they do convey, in scenes with her husband and with Théo, is Anne’s complex psychological process during the act. Occasionally, during moments of lovemaking or while talking with Théo, the camera doesn’t even show Anne’s face at all, ascribing to viewers her perspective instead, connecting us directly to the female gaze.

While Ms. Breillat withholds judgment of Anne, the plot does reach a moral standoff when her sister finds out about the affair, and Anne subsequently breaks it off with Théo. The young man, though, proceeds to tell his father and the confrontation scene between Pierre and Anne is one not soon forgotten. Suffice to say, the film is not your typical light French summertime drama in which secrets are revealed and transgressions condoned.

Or is it? One of the most intriguing elements of “Last Summer” is how it juxtaposes Anne’s no-nonsense work as an attorney specializing in cases involving families and young women with romantic settings and almost-satirical luxuries. In nearly every scene, Anne wears form-fitting yet tasteful dresses with plummy pumps or high heels, and even sports a glass of wine in her hand several times. She also drives a chic, pale blue Mercedes convertible everywhere. 

Could Ms. Breillat be critiquing liberal guilt and suggesting that upper class values merely mask carnal and destructive tendencies? Is the film a twisted take on President Macron’s early days with teacher Brigitte Trogneux, who later became his wife? 

We’re meant to see Anne as both a responsible adult and a bit of a rebel, as a sympathetic figure (a few stray lines hint at a traumatic sexual encounter in her past) and a corrupter of youth. This uncertain duality as both heroine and anti-heroine gives Ms. Drucker the role of a lifetime, with the actress imbuing Anne not with tortured energy but a stillness that is both shocking in its effrontery and disturbing in its ease. Much like her director, she delves into the darker parts of a woman’s psyche with keenness and more than a little pleasure.