The sun doesn’t appear to come out much in “South Mountain,” despite the fact Hilary Brougher’s enthralling drama is set over the course of one summer in the Catskills. It should be a happy time for Lila (Talia Balsam) to have everyone under one roof, sitting alongside her best friend Gigi (Andrus Nichols) and her husband Edgar (Scott Cohen) kick back on the porch, while Gigi’s daughter Charlotte (Violet Rea) and her daughter Dara (Naian Gonzalez Norvind), best friends in their own right, fan out into the nearby woods and Sam (Macaulee Rusnak Cassady), Edgar’s college-aged daughter from a previous marriage that Lila has come to call her own, appears happy when arriving with a new friend named Jonah (Michael Oberholtzer). The adorable garden that sits besides the country home is evidence of the time and care Lila puts into things and it’s obvious she’s paid just as much attention to cultivating a modest yet ideal life for herself.

Still, “South Mountain” offers up every frame with a dark tint that one comes to recognize as reflecting the rot that threatens to ruin the harvest, as Edgar can be seen sneaking off under the pretense of a screenwriting gig for decidedly unprofessional reasons and it’s casually mentioned that Gigi will soon be going in for cancer treatments. Embracing the deep, tactile blacks cinematographer Ethan Mass finds through using natural light, such potentially dreary material is exhilarating in the hands of Brougher, who reminds audiences of her envelope-pushing breakthrough “Stephanie Daley,” in which she turned the paralysis of a teen (Amber Tamblyn) grappling with an unwanted pregnancy, into a gripping thriller. Although Lila is well past worrying about the future because of all its unknowns, a considerable part of the intriguing conflict of “South Mountain” comes from what she knows all too well, negotiating what personal pain and embarrassment she’s willing to accept in order to keep her routine intact as the people around her begin to let her down.

While Lila staves off a feeling of defeat, Balsam takes an ownership of the character in a way that’s electrifying to behold, suggesting that other filmmakers who have deployed her instant gravitas in smaller doses have done so out of concern an audience might not be able to take it. With a wonderfully slippery Cohen as Lila’s foil, the film is constantly surprising in terms of how frank characters gradually address one another, as brutal honesty becomes the only way to nail each other down, and Brougher’s master stroke is creating an elusive sense of time, noting the specific days when scenes take place to quietly observe a nugget of information dropped on July 12th builds into a shiv used on August 24th to end an argument. The writer/director infuses rich, granular details more commonly associated with literature where even in a lean 85 minutes, you not only witness what might well be the end of relationships that have meant the most to Lila, but come to understand all the highs and lows that have led to the present moment. Aware of the totality of what she’s done, Brougher gives a moment to the audience to let it all settle, letting the sound of nature surround you before the end credits roll — it’s a beautiful touch, though by then you’ve already been enraptured, seeing how wild human nature can be.

“South Mountain” will screen at SXSW on March 12th at the Alamo Lamar B at 3:15 pm and on March 14th at 6 pm at the Alamo Lamar C.