There is a prescient shot that opens “Let Him Go,” the frontier drama starring Kevin Costner and Diane Lane. A flat stretch of Montana plain, a blanket of blue-gray sky, as if Heaven itself was just beyond the horizon. It is haunting, that endless horizon. Thomas Bezucha, who directs, holds the shot long enough to get you thinking. Cinematographer Guy Godfree, with a Canadian Screen Award under his belt, shoots the film. Between them, country becomes desert. It’s the Midwest version of the Wild West—trees, grass, and streams replace sand dunes in Bezucha’s adaptation of Larry Watson’s novel.

Bezucha, who took on Midwest romance in “Big Eden,” is well suited to tackle the material. But the film is not so much a retelling of the story as an interpretation. Using Watson’s book, which is based on true events, Bechuza plays with the flexibility of “Let Him Go,” imbuing the action-packed premise with a poetic tone fit for a Western.

“Let Him Go” is a tale of loss and lost souls, and of families riding it out. It opens with George and Margaret Blackledge (Costner and Lane, respectively) reeling from the death of their newly married son. His widow, Lorna (Kayli Carter), remarries into a family of bad apples, the Weboys. In town one day, Margaret spies her grandson’s new stepfather smacking Lorna around. Days later, the family relocates from Montana to North Dakota, where they live in a house just outside of town. It’s no place for a child (or anyone, really) which leads Margaret and George to devise a plan: buy a gun, find the boy, ride off into the sunset. What could go wrong?

Enter Blanche Weboy (Lesley Manville). With a penchant for smoking, cursing, and raising her children like wolves, hungry for the scent of blood, Manville is having some fun as the ultimate evil mom, hardened by the punishing lifestyle of mid-century farm life. She rules her pack of violent, lawless boys with an iron fist, and she has no intention of giving up her newest family member, the grandson.

The Blackledge’s journey takes them down a path of wickedness, pounded, beaten, and drilled into this small town, and the way the Weboys carry themselves, North Dakota could sue for slander. The opposition to the Weboys is Margaret. She’s the type of woman who treats everyone like family, who politely smiles when Blanche throws shade at her parenting, although she’s no badass. Margaret, denied her grandson, isn’t afraid to use her revolver.

The emotional core of the film is the relationship between Lane and Costner, and they are certainly easy to root for. They’re the only two actors who seem to be playing real people, though the supporting cast does a great job playing archetypes. As Bill, Blanche’s brother-in-law, Jeffery Donovan is GIF-worthy. Is his crazed performance funny or menacing? Either way, you can’t take your eyes off him. Rounding out the cast is Will Britain, Will Hockman, and Booboo Stewart as Peter, a young Native American who the Blackledges encounter.

But this is Lane’s movie, hands down. The actress is magnetic as yet another woman who refuses to be bound by gender conventions. This particular body of work began with her breakout in 1979 as the smarter-than-her-male-counterpart love interest in “A Little Romance.” She was on the cover of Time Magazine. The next role came in 2002 with “Unfaithful,” the rare romance where the woman cheats on the man.

The Western may headline tough guys like John Wayne and Clint Eastwood, and Costner may be the grittier presence on screen. But it’s Lane who saddles up for top-billing, and its Lane who rides off into that elusive, endless horizon. [B]

“Let Him Go” arrives in theaters on November 6.