“Growing up we were so indoctrinated with the big sky thing … I really bought it.” This disabused observation comes courtesy of Erin (Haley Lu Richardson), one of the two main characters in “Montana Story,” a new film written and directed by Scott McGehee and David Siegel.

Erin is a cook living in upstate New York who has, after seven years away, returned to her home in Paradise Valley, Montana. The circumstances there are dire: Her father lies in a coma on life support.

Her half-brother Cal (Owen Teague) is already at the ranch, having traveled from not-so-distant Wyoming. On hand at the homestead are Valentina (Kimberly Guerrero), the family’s longtime housekeeper, and a hospice nurse (Gilbert Owuor) who goes by the name Ace.

We learn about Erin and Cal’s father, Wade (Rob Story), in bits and pieces; what details emerge aren’t flattering. In the meantime, the cost of Wade’s health care has Cal scrambling to pay. All of the family possessions, including their sizable estate, will have to be sold. Before being felled by a stroke, Wade was a successful lawyer, albeit one who engaged in some dodgy practices. 

Dodgy, too, was his parenting, the excesses of which account for Erin’s running away at age 18. The relationship between brother and sister is similarly strained. Cal is, in fact, shocked that Erin has come to visit after having cut off all communication since leaving home. Erin is equally shocked, as well as emotionally unprepared, by the state of her father. Within an hour, she hails a Lyft to hightail it out of Montana.

The only thing Cal and Erin have in common, other than a fondness for Valentina and her son Joey (a loose-limbed Asivak Koostachin), is Mr. T., a 25-year old stallion whose days are numbered. Their love for Mr. T. is such that Cal visits the horse before looking in on dad, and Erin starts making arrangements to take the animal back to New York. Better that than being put down.

The portion of “Montana Story” that outlines Erin’s quixotic venture with Mr. T. is the most engaging. Cal and Erin drive some miles out-of-town to meet Mukki (Eugene Black Rock), a figure of dubious repute who’s selling a car and trailer that will, ostensibly, bring the beloved stallion back east. Mukki is more charming than he is honest, and Erin gets sold a bill of goods.

Erin subsequently cuts Mukki a considerable amount of slack, and one can’t help but feel that it is Mr. Black Rock, more so than his sly character, that occasions this generosity. With his dry, can-do demeanor, he holds the screen like no one else in “Montana Story.” We miss Mukki when he’s off-screen.

It isn’t a slight to the movie — or much of a slight, anyway — to state that the supporting cast outshines Ms. Richardson and Mr. Teague. They’re both solid playing characters who are saddled with a fair share of foibles, but the script lets them down by capitulating to catharsis and, with it, settling for a homespun predictability. In comparison, the tension generated by Mr. Owuor and Ms. Guerrero, both of whom play characters who keep their not inconsiderable emotions in check, carries more dramatic integrity.

The real star of this movie is Montana itself. Contrary to Erin’s grousing, that “big sky thing” is for real. Messrs. McGehee and Siegel, along with their invaluable cinematographer Giles Nuttgens, don’t lavish attention on the landscape so much as confirm its scarifying independence. They partake of the awe — and humility — that is engendered by the mountains, the valleys, and, yes, that big sky. 

In doing so, the proverbial hill of beans that is three little people isn’t amplified or concentrated so much as diminished. Having said that, “Montana Story” is, in the end, an honorable addition to the cinematic corpus of American life, a film to be placed alongside “Minari,” “The Rider,” and other mainstays of the genre.