The line between fiction and real life has always been a bit blurred in Safdie productions, employing as they do a loose-limbed shooting style and streetwise physical production drawing on real locations and, sometimes, unsuspecting passersby. But this elision is particularly acute in their latest film, Heaven Knows What, which was literally borne of a chance encounter. While researching Uncut Gems, a larger-budget film set in New York’s midtown Diamond District, Josh spied on the street the 19-year-old Arielle Holmes. She had giant round eyes and high cheekbones, was wearing cut-off jeans and a comic book T-shirt, and seemed somehow different from the street kids he’d normally come across. She was also a heroin addict in a tumultuous relationship with another homeless youth, Ilya, and, upon hearing her tale, Josh encouraged her to write it down. Those pages — an unpublished memoir titled Mad Love in New York City — became the basis for the brothers’ quickly realized Heaven Knows What, co-scripted by regular collaborator Ronald Bronstein and shot by Sean Price Williams. At the film’s start, Holmes’s character Harley is goaded by Ilya — played with a brooding, chilling intensity by Caleb Landry Jones — into the ultimate gesture of destructive romance: suicide. Her attempt fails, however, and when she’s released from Bellevue, she returns to her habit, this time with a new supportive friend, Mike (Buddy Durress). The volatile Ilya, however, is always somewhere around the corner.

With a trippy, audacious score and a bravura, long-take sequence that’s the Safdies’ boldest filmmaking yet, Heaven Knows What is a realistic, wisely observed, piercingly authentic look at drug-addicted homeless youth. It’s also deeply empathetic toward its characters, infusing their lives, lived in pockets of the city New Yorkers walk by every day, with a near-operatic intensity. (Scott Macaulay)