In the Belgian drama “The Unknown Girl,” the latest slice of realistic drama from Belgium’s Dardenne brothers, a young doctor’s guilt, ambition and stubbornness are put in play in a search for justice and closure.

Jenny Davin (Adèle Haenel) is temporarily running a retired doctor’s general practice in Liege, Belgium — taking in everyone from babies to old folks in an impoverished neighborhood near the expressway. One night, the doorbell goes off, and Jenny tells her intern, Julien (Olivier Bonnaud), not to answer it, because it’s already an hour past closing time.

The next morning, as Jenny opens the office, she’s approached by two police detectives. A young African woman was found dead by the river nearby, and the cops would like to check the office’s surveillance-camera footage to see if they can retrace the woman’s last hours. Sure enough, the footage shows the woman was the one who rang Jenny’s doorbell, desperate for protection from whoever was chasing her.

Jenny, feeling guilty that she could have helped this woman, becomes obsessed with finding out more about her — to the point where she gives up her new position at a well-heeled medical partnership to keep the old doctor’s practice. She takes the woman’s photo around the neighborhood, but nobody recognizes her. The closer Jenny gets to the truth, the more resistance, and threats, she receives.

She focuses on Bryan (Louka Minnella), a teen she treats for stomach issues. She becomes convinced that Bryan knows the woman, but is holding back because of his father (played by Jérémie Renier, a regular in the Dardennes’ films going back to “La Promesse” in 1996).

While searching for the dead woman’s identity, Jenny also handles the day-to-day problems of her patents. And she must contend with Julien’s abrupt decision to quit medicine, just ahead of his final exams, and return to his rural village.

The writing-directing team of Jean-Pierre and Luc Dardenne have made a career of gritty, ground-level dramas about people grappling with working-class issues. Here, they plunge the unsuspecting Jenny into the underground economies of Belgium’s poor and immigrant people, and she learns some harsh lessons about prostitution, under-the-table businesses and other crime that her patients have to dodge every day.

Buoyed by a quietly intense performance by Haenel, “The Unknown Girl” delivers a clear-eyed and gut-wrenching look inside the lives of Europe’s downtrodden, whose problems are bigger than one well-meaning doctor can fix.

* * * 1/2

’The Unknown Girl’

A young doctor searches for the identity of a woman whose life she might have saved in this moving drama by the Dardenne brothers.

Where • Broadway Centre Cinemas.

When • Opens Friday, Sept. 29.

Rating • Not rated, but probably R for language, sexual content and violence.

Running time • 113 minutes; in French with subtitles.