In Jean Pierre and Luc Dardenne’s very best films, you know exactly what you’re getting — until the quiet dramatic pivot that gently ensures you don’t. In “The Unknown Girl,” only the first half of that assessment is true, though what we get is largely exemplary: a simple but urgent objective threaded with needling observations of social imbalance, a camera that gazes with steady intent into story-bearing faces, and an especially riveting example of one in their gifted, toughly tranquil leading lady Adèle Haenel. What’s missing, however, from this stoically humane procedural tale of a guilt-racked GP investigating a nameless passer-by’s passing, is any great sense of narrative or emotional surprise: It’s a film that skilfully makes us feel precisely what we expect to feel from moment to moment, up to and including the long-forestalled waterworks. Though it will receive the broad distribution practically guaranteed the Belgian brothers’ work these days, the film is unlikely to prove one of their sensations — more the healthy arthouse equivalent of a biennial checkup.

It may follow in the Dardennes’ tradition of sensibly prosaic titles, but “The Unknown Girl” would also be a good fit for a film noir — which, in a thoroughly dressed-down, cleanly lit way, their tenth feature kind of is. Though it benefited from a performance of unvarnished authenticity by Marion Cotillard, 2014’s “Two Days, One Night” was arguably the brothers’ most narratively contrived film to date, built on a neat structure of staggered confrontations that eventually yielded the required catharsis. Landing with critics, audiences and even Academy voters alike, it was a successful shift in register, so it’s not altogether surprising to see them now meshing their signature social realism with tentative genre trappings.

She may tote a stethoscope rather than a handgun, and favors a particularly shaggy plaid variation on a trenchcoat, but fresh-faced Dr. Jenny Davin (Haenel) is, to all intents and purposes, the protagonist in an old-school, hard-boiled detective movie — right down to her fixation on the face of a dead woman whom she has only seen in images (or, in this case, an agonizingly short burst of CCTV footage). The woman in question, unidentified for much of the running time, is evidently an African immigrant, captured banging desperately one evening on the front door of Davin’s surgery in Liège; shortly afterwards, she’s found dead of a fractured skull in the banks of the Meuse. As the police, devoid of leads, turn to Davin for details, she realises with horror that she was in during the woman’s attempted after-hours entrance — and remembers deliberately ignoring the buzzer.

Unable to shake the idea that answering the door might have saved the woman’s life, and distraught at the idea of her being buried without a name, Davin embarks on an insistent amateur investigation of her own. It’s one that leads her to skim the drab surface of Liège’s underworld, but more often into the modest homes of local residents — her own patients among them. Mixing some gumshoe work into her house calls, she demonstrates an interrogation style as calm and unflappable as her bedside manner. “Emotional involvement leads to a bad diagnosis,” she chides her less assured intern Julien (newcomer Olivier Bonnaud) near the start of proceedings, though Davin finds it increasingly difficult to maintain that clinical distance as her non-medical quest pushes on toward a moving but mostly expected resolution.

The Dardennes’ typically unfussy, clear-spoken script breaks up the grim determination of Davin’s search with regular vignettes from her working day. Each one extends our understanding of the city’s hard-wearing social fabric, be it a middle-class teen resiliently battling leukemia or a language-challenged burn victim who fears deportation if he visits a hospital for his grievous injuries. Though the film resists direct political or administrative commentary, Davin tellingly rejects a loftier hospital appointment in favor of maintaining a threatened practice for patients on medical insurance rates. The gulf between her generally unimpeachable virtue as a doctor and the moral self-loathing she feels over once turning a blind eye to one in need, however, is heavily inscribed throughout, while a subplot that sees her attempting to revive a disenchanted Julien’s passion for medicine is rather too patly drawn.

Though “The Unknown Woman” features a veritable alumni gathering of past and regular players from the Dardennes’ films — Olivier Gourmet, Fabrizio Rongione, Jérémie Renier, Thomas Doret, Jean-Michel Bathazar — in roles that range from passingly to piquantly minor, the film serves chiefly as a showcase for the wonderful Haenel. Proving, in her first collaboration with the brothers, an intuitive thespian match for their delicate, not-overly-demonstrative emotional intelligence, she works softly against the grain of her character’s general goodness — playing up the moments of cold internal panic and silent judgment that lead her, not always fairly, to doubt her own compassion.

As ever, the Dardennes’ filmmaking proves serenely accomplished in deflecting attention away from itself. Alain Marcoen’s even-keeled, easy-breathing lensing often achieves the effect of complete stillness while understatedly directing the viewer’s gaze to fine, expressive details of an actor’s countenance. Marie-Hélène Dozo’s editing likewise shapes and paces human encounters in ways that feel entirely organic, working up anxious cinematic tension without ever seeming beholden to a rigid storytelling structure. The Dardennes may not currently be working in a vein of the strictest realism, but the results still feel markedly, airily natural.