It's the 1960s and Margaret (DIANE LANE) and George Blackledge (KEVIN COSTNER) are still grieving over the accidental death of their 25-year-old son, James (RYAN BRUCE), a few years back. Now making matters worse, the young man's widow, Lorna (KAYLIE CARTER), has married the less-than-upstanding Donnie Weboy (WILLIAM BRITTAIN) who's decided to take her and his young stepson, Jimmy (OTTO & BRAM HORNUNG), from Montana to North Dakota to live with his family.

Despite having no legal standing, Margaret isn't going to idly stand by and thus makes the ultimatum that she's going to travel there and bring her grandson back home, something that doesn't sit well with George, what with him being a former career lawman.

Nonetheless, and to keep her safe, he goes along for the trip, hoping that given the chance to see that their grandson is okay she'll change her mind. Along the way, they end up meeting Native American loner Peter Dragswolf (BOOBOO STEWART) who knows of the Weboy clan and warns the grandparents that they better be careful.

After meeting Donnie's friendly but somewhat creepy uncle, Bill (JEFFREY DONOVAN), they head off to the home of the clan's matriarch, Blanche (LESLEY MANVILLE), who doesn't take kindly to the visit or Margaret's attitude. From that point on, it's unclear how far the two women will go to retain or retake custody of the young boy.

If there's one constant in life beyond the commonly stated ones of visits by the taxman and eventually the Grim Reaper, it's that everyone is going to experience loss. And that comes in all sorts of shapes and sizes throughout one's life. There's the loss of childhood innocence, and of contests or sporting events one's either involved in or rooting for, and sometimes the loss of one's freedoms or bodily senses or functions.

Of course, the greatest loss is that related to death, be that of a beloved pet, friend, or family member. And people respond to that gravest sort of loss in all sorts of ways, one of which is not wanting to let go despite understanding what's happened.

For some, that's continuing to act as if the dearly departed are still around, or not wanting to put away, box up, or donate that which belonged to the deceased. And sometimes that's holding onto whatever was nearest and dearest to them, in the belief that doing so will somehow mean keeping some part of that pet or person alive in a non-literal sense.

That's certainly the case in the aptly named "Let Him Go" where Diane Lane plays Margaret, an early 1960s woman who's trying to help her adult son's wife, Lorna (Kaylie Carter), get the hang of relatively new motherhood. But then on an otherwise unremarkable, ordinary day, the son is thrown from his horse, lands on a bunch of rocks, and dies.

We next see Margaret and her husband, George (Kevin Costner), understandably looking stunned as they dress for what writer/director Thomas Bezucha has us believe is the subsequent funeral. Instead, we've jumped forward in time a bit and it's for the upcoming nuptials between Lorna and her boyfriend, Donnie (William Brittain). Thus, it's not long before Lorna moves out of her in-laws' house and into Donnie's apartment in town with her now slightly older son, Jimmy (played by Otto and Bram Hornung).

While sad not to have her grandson living with her, Margaret at least knows the boy -- and thus the remaining connection with her son -- is nearby and easy to visit or have over at the house. But then she witnesses Donnie publicly abuse his new wife and stepson and before she can do anything, she's shocked to learn that all three have left town in the dark of night to go live with his mother in a nearby state.

Not willing to lose contact with her grandson, she decides she's going to go find him, with George -- a former career lawman -- reluctantly going along for the trip, mainly to protect and support his stubborn better half with hopes that doing so will allow her to do as the title says.

But they soon learn -- including via a bit of cautionary advice they receive from a loner Native American, Peter (Booboo Stewart), who they meet on their trek -- that the Weboy clan is not to be messed with. With that especially being true of the matriarch of the clan, Blanche (Lesley Manville), who rules over her three adult sons, smiley-creepy brother (Jeffrey Donovan) and her daughter-in-law and grandson now that they've been brought into the fold.

For most of the film, Lane and Costner -- who previously were paired together as another wife and husband duo in "Man of Steel" -- make this drama -- where the title refers to a number of people and even a pet horse -- work quite well. The veteran performers more than make for a believable couple of that bygone era and you can easily sense and understand their loss on several fronts.

But then Bezucha opts to segue out of the family drama genre into that of the suspense thriller one along the lines of "Taken" and Mr. Neeson's other such "give me back what's mine or else you'll experience my particular set of skills" cinematic offerings. No, Martha and Jonathan, um, Margaret and George can't call on their "super man" to save the day, and thus they must resolve things on their own.

Alas, that's when the storyline jumps the rails as I didn't buy into the logic of their actions, particularly with their former daughter-in-law and grandson not being held against their will, at least technically or in a manner that would stand up in a court of law while trying to defend the tactics that are ultimately deployed on the "rescue mission."

It doesn't derail the entire offering, and on its own, the action-laced finale certainly works in a "Taken" sort of retributory meets vigilante sort of way. But it definitely gives the overall film the feeling of being a mash-up of two different genres lacking credible behavior in the end. That's particularly with Costner's character who certainly understands how the law works, with not enough related material present to sell his actions as sacrificial for the sake of his wife and grandson (if that's the storytelling intent).

Yes, people react to loss in all sorts of ways, sometimes unexpected. I just didn't buy how things ultimately play out here beyond the cathartic experience of watching bad people get theirs. With the first and second act buoying what follows, "Let Him Go" is decent enough to rate as a 6 out of 10.