Diane Lane and Kevin Costner reunite on screen, only this time it’s not as the earthy and earthly parents to Superman (Man of Steel, 2013). Instead, Let Him Go, from writer-director Thomas Bezucha (The Family Stone, 2005), based on Larry Watson’s 2013 novel, features the two stars as a long-time married couple, Margaret and George Blackledge, living a peaceful existence on their Montana ranch.

Well, it’s peaceful for now, as George is retired from his career as a lawman. Their son James (Ryan Bruce), his wife Lorna (Kayli Carter, “Godless”), and grandson Jimmy live on the ranch with Margaret and George. Grandma Margaret’s devotion to her grandson and judgmental nature sometimes crosses the line, creating quiet tension with his mother Lorna. George’s trained eye sees it all, but he mostly keeps his thoughts private, although the communication he shares with Margaret is often through a simple gesture or nod. Their chemistry is one that’s only built through time (and fine acting).

When a freak accident leaves James dead, we flash forward three years as Margaret and George attend Lorna’s wedding to Donnie Weboy (Will Brittain, who was excellent in this year’s Blow the Man Down). George senses that Donnie does not possess the highest moral character, but Margaret is hit hardest by the newlyweds moving off the ranch and taking her beloved grandson with them. Concern escalates quickly when Margaret witnesses Donnie being physically abusive to Lorna and Jimmy, and then he relocates them to North Dakota to be near his family…without so much as a warning or goodbye to Margaret and George.

Crossing Grandma Margaret is like kicking the hornet’s nest. Poor George arrives home one day to find the car packed and Margaret on a mission to bring Jimmy home. George’s feeble attempt to reason with her fails (as he knew it would) and the two are soon on the road through some gorgeous countryside captured by cinematographer Guy Godfree. Along the way, they cross paths and befriend Peter (Booboo Stewart), a Native American who deserted “Indian School” for a life of solitude on the plains. It’s also on this road trip where Margaret and George are inundated with every possible warning about the notorious Weboy clan of North Dakota. No specifics are provided, but the message is clear…no one messes with the Weboys.

A tip leads the grandparents to Bill Weboy (Jeffrey Donovan, “Burn Notice”), and he provides living proof that the Weboy clan is rotten to the core. Behind an evil grin, Bill invites Margaret and George to the family ranch for dinner and a visit with their grandson. At the ranch, we are introduced to the twisted matriarch, Blanche Weboy (Lesley Manville, Phantom Thread, 2017). This meeting of the families is about as tense as any we’ve seen on screen. A clash of good versus evil is always welcome, which makes it so disappointing that a film so stellar to this point, abruptly shifts from an intriguing psychological thriller into a ludicrous circus of violence, poor decisions, and absurdity.

There is a lot to like here, before it spins off the axis. Diane Lane is ferocious in the role, and Costner is very effective as her ‘still waters’ husband. It’s a hoot to see Ms. Manville lose her British accent and go over-the-top as nasty Blanche, and the early 1960’s setting looks great, including the vehicles. As mentioned before, the scenery is breath-taking, with Alberta (Canada) standing in beautifully for Montana and North Dakota. Composer Michael Giacchino is more accustomed to working on superhero and animated movies, and the score is often distracting in the first half, but fits better in the final act. Brace yourself for a couple of tough-to-watch scenes and a jarring tonal shift.