NEW YORK (CNS) — In May 2010, when 24-year-old prostitute Shannan Gilbert disappeared in the gated Oak Beach community of New York's Suffolk County, the search for her led police to a set of gruesome discoveries. Four young women were found strangled to death by someone later identified as the Long Island Serial Killer.

Having debuted at the Sundance Film Festival in January and streaming now on Netflix, the gritty and powerful 95-minute feature "Lost Girls" details the late Mari Gilbert's (Amy Ryan) tenacious pursuit of justice for her murdered daughter.

In crafting her first narrative movie, director Liz Garbus — previously known for her award-winning documentaries, including 1998's "The Farm: Angola, USA" — invests "Lost Girls" with important social commentary that elevates it above more run-of-the-mill crime procedurals.

Screenwriter Michael Werwie adapts his script, marked by sharp dialogue, from journalist Robert Kolker's eponymous 2013 book, an acclaimed bestseller subtitled "An Unsolved American Mystery."

Besides the prostitution and murder themes already noted, the film also contains frequent vulgarity, references to drug use and portrayals of mental illness. While sex trafficking and violent death figure prominently in the narrative, the picture emphasizes the subsequent investigation, not the depiction of these lurid crimes.

Thus, although "Lost Girls" is definitely for adult viewers only, they will find it more restrained than other shows of its kind. (The Motion Picture Association rating is R — restricted. Under 17 requires ac-companying parent or adult guardian.)

In the rural Catskill Mountains village of Ellenville, New York, cash-strapped blue-collar worker Mari is disappointed and frustrated to be cut from job shifts she can't afford to lose. But news that her oldest daughter Shannan (Sarah Wisser) is driving up from Jersey City for dinner improves the single mother's mood.

Shannan, though, never turns up and Mari doesn't hear back from her. So, accompanied by her teen daughters, Sherre (Thomasin McKenzie) and Sarra (Oona Laurence), Mari travels to Shannan's home town to see what has happened to her. Obtaining Shannan's phone logs from the police, the family dis-covers she made an extended 911 call in Oak Beach.

There, Mari quickly establishes herself with the county's police commissioner, Richard Dormer (Gabriel Byrne), as someone he shouldn't cross. "I have a talent for holding grudges," she says, "and unless you help me, I'm gonna raise more hell than you can handle."

When law enforcement officials repeatedly refer to her daughter as a prostitute, the advocate objects. "It's never friend, sister, mother, daughter," she says. "It's our job as mothers and sisters to make sure these girls are not forgotten."

Despite their identification of her as a sex worker, however, the investigators ironically fail to connect Shannan's demise to the other deaths by strangulation. This naturally vexes Mari, who demands of Dormer: "Is this some kind of cover-up or just incompetence?"

The case remains unsolved, and the film's postscript indicates that the Long Island Serial Killer ulti-mately murdered between 10 and 16 women.

To its credit, "Lost Girls" challenges its audience to see Shannan's life as more than the sum of her worst choices. As the drama unfolds, viewers learn more about Shannan's troubled history, which deepens to their understanding and engenders greater compassion toward her.

Recounting to Dormer Shannan's struggles with bipolar disorder and bulimia, Mari recalls how she "ran out into the snow one night with no clothes on and nearly froze to death while I was working graveyards and doubles just to keep the lights on."

The film also successfully exposes societal fissures dividing working-class people from the affluent. Like other similarly situated families, the Gilberts can't get help to prevent tragedies and the police afterward dismiss their demands for justice. Yet the gates and walls of Oak Beach serve to insulate its wealthy res-idents from any accountability.

Formidable yet vulnerable, Ryan is commanding as Mari. Having made an impressive debut in the 2018 film "Leave No Trace," young New Zealand-born actress McKenzie also shines as Sherre.

By draining the starkly beautiful seaside landscape against which "Lost Girls" unfolds of its color and casting a pall over it, Igor Martinovic's cinematography achieves a distinctive look. Yet this dark setting often attenuates viewers' capacity to make out the action as clearly as they might wish.

That's merely a cavil, however. As it highlights salient concerns about injustice, inequality and our col-lective failure to protect the most vulnerable among us, "Lost Girls" registers as a refreshingly serious movie for grownups.