Producers: Andrew D. Corkin, Christopher Sparling, Alex Lalonde, Zack Schiller, David Boies, Naomi Watts, Chris Parker and Dylan Sellers   Director: Phillip Noyce   Screenplay: Christopher Sparling  Cast: Naomi Watts, Colton Gobbo, Sierra Maltby, Debra Wilson, Woodrow Schrieber and David Reale    Distributor: Vertical Entertainment

Grade: C-

Films about school shootings have become almost as numerous as the ghastly events themselves, but this one attempts a different perspective than most—that of a mother alone and far removed from the tragedy who nevertheless becomes directly involved in it.  “The Desperate Hour,” originally titled “Lakeview,” is an initially interesting exercise in virtually one-person cinema that unfortunately devolves into an overly melodramatic and increasingly absurd last act.

Naomi Watts is Amy Carr, who’s introduced getting her young daughter Emily (Sierra Maltby) off to school and prodding her teen son Noah (Colton Gobbo) to get up and go to Lakeview High.  She then sets off on a run that takes her deep into the woods.  Her only companion is her smart phone, which she uses to listen to music as she goes, but also proves absolutely essential in keeping her in touch with the outside world.

We learn a number of things via the incessant calls she takes early on.  (With the exception of Amy, Noah and Emily, virtually all the characters are disembodied voices on her line.)  Her husband was killed in an auto accident a year earlier, and the loss has hit Noah especially hard, turning him into a surly, distant lad.  And her parents are going off on a trip, and she’s to pick up their car from the shop.  She also gets a call from Emily, asking her to deliver a plaster dinosaur she’d made in a crafts course for a school event.

One gets the sense that Amy’s overburdened and rather depressed herself, not least because of the constant presence of that phone, but any self-absorption she might be feeling dissipates when police cars start speeding toward town on the otherwise empty road and she gets an emergency message that something has happened at one of the schools, all of which have gone into lockdown as a result.  She tries frantically to get information from the police, from emergency operators, from the staff at Emily’s elementary, and from friends, but she’s told simply to make her way to the community center where distraught parents are congregating.  Of course, she’s miles away from either home or the center, and without transportation.  Eventually she’ll order a Lyft drive, but it’s delayed by the congestion on the roads.

And she can’t get in touch with Noah, though she learns that he did in fact to go school, and that it was there that a shooting has occurred, with the incident not yet resolved.  She’s obviously concerned about him, but becomes more so when a policeman contacts her with questions.  Could he be a victim?  Or the perpetrator?

Last year’s “Mass” offered a probing examination of the perspectives of two mothers—the one of the victim of a school shooting, the other of the shooter—but at a distance of years, in the form of a conversation.  The fact that “The Desperate Hour” is presented contemporaneously from the viewpoint of a woman who might be either makes for a potentially intriguing complement to that well-acted film, and for a while it seems ready to fulfill on its promise.

But scripter Christopher Sparling, who had already made a movie in which the main characters are a distressed person and a cell phone (2010’s “Buried,” in which Ryan Reynolds was as committed as Watts is here), flubs the potential by moving into dumb thriller mode and piling up so much implausibility in his desire to ratchet up the tension that one is inclined to dismiss the whole exercise as divorced from the sense of fraught reality that Watts, director Philip Noyce and his technical team—particularly cinematographer John Brawley, editor Lee Haugen and composer Fil Eisler—are striving to maintain.

One can swallow the predictable spill that Amy takes on the rough terrain, resulting in her jogging along with a limp—a mother would endure any pain in such a circumstance, after all.  One can even accept the persistently considerate treatment by an emergency operator.  But when she enlists a clerk at the auto shop, which just happens to be close to the high school, to provide regular reports on what’s going on there, your willingness to suspend disbelief will probably reach the breaking point.  And you’re likely to slip into sheer incredulity when, by calling a co-worker, Amy manages to make herself a direct participant in the unfolding drama, beating even the cops to the punch.  She becomes what might be called a super-smartphone mom.  And with respect to what’s happening in the school, the film is alternately clichéd and crudely manipulative. The ending is as well, and made even worse by an insert in the closing credits that has all the punch of a public service ad.

Despite that last-minute admonition, in the end “The Desperate Hour” comes off more as an exploitation of an endemic national tragedy than a serious dramatization of it.