Even those who find Mormonism a strange, even slightly sinister religion may be offended by this movie, which depicts a group of adherents (and ultimately their leader Brigham Young) as responsible for the so-called Mountain Meadows Massacre of 1857, in which a wagon train of passing settlers was almost wiped out while crossing through Utah on the way to California. Not because the narrative that Carole Whang Schutter and Christopher Cain (who also directed) is necessarily speculative in many respects, and moreover adds a sappy puppy-love story to the mix. Nor because, by prominently noting the date of the episode as September 11, it feeds rather crudely on more recent tragedy. But simply because “September Dawn” has the quality of a mediocre TV movie. It’s like watching a small town’s scruffy historical pageant rather than a professionally-produced feature.

The details of the incident at the center of the movie are the subject of continuing debate, but the central facts aren’t in dispute. A convoy of wagons from Arkansas (and probably Missouri), led by Alexander Fancher, entered Utah in the summer of 1857 on the way to California and, after a stay at Salt Lake City, proceeded into southwestern Utah, an area of Mormon settlement. At the time the region was on edge: word had arrived of the murder of a Mormon apostle in Arkansas the preceding May, and the Mormon settlers were preparing for an assault from federal forces; church leader and territorial governor Young had declared the area under martial law. The locals saw the travelers as interlopers and their militia apparently joined with Paiute fighters to attack the train as it rested at Mountain Meadows on September 7. The party defended itself for several days, but on September 11 militiaman John Lee approached the travelers and persuaded them to disarm, promising them safety, but ordered their massacre after they did so. Lee would later be tried, convicted of murder and executed. But it has never been definitively proven that Young had known of the attack in advance or approved it, though there’s a very good chance he did.

This film, however, portrays it as certain that he did; here Young, in the person of Terrence Stamp, who plays him in a few isolated scenes as a scowling fanatic, orders the massacre and duplicitously covers up his involvement. On the other hand, though it includes Lee as a character—he’s played by Jon Gries—(and shows his execution), the major on-site instigator of the slaughter is portrayed as Bishop Jacob Samuelson (Jon Voight), a fictional figure who lulls the gullible travelers, most notably Fancher (Shaun Johnston) into a false sense of security while planning their murder. And in a crackpot Romeo-and-Juliet plot twist, the script posits a romance between Jonathan (Trent Ford), one of Samuelson’s sons, and pretty Emily Hudson (Tamara Hope), the daughter of the kind-hearted preacher who’s part of the “gentile” group. Jonathan’s supposed to be the audience-pleasing sensitive boy who’s attracted not only by Emily’s beauty but by the genial good nature of Fancher and his group, in contrast to his father’s brutal sternness, and who has to be confined to keep from warning the travelers. On the other hand, his younger brother Micah (Taylor Handley), though conflicted at what’s demanded of him, eventually participates in the slaughter in Indian garb, with terrible psychological result.

Clearly “September Dawn” is constructed as an anti-Mormon diatribe disguised as a historical narrative, with some sappy romantic elements added as a sort of “West Side Story” in chaps. But even if one were appalled by such a concept for a film, he would still have to recognize any technical proficiency exhibited by the result. In this case, however, that’s not necessary, because the movie is a clumsy, amateurish effort. The performances are poor—the youngsters are either wan (Hope, Ford) or overwrought (Handley), and old pro Voight, with a little goatee that gives him a Mephistophelean air, vacillates between nostril-flaring scenery-chewing and pallid underplaying, which is somehow even worse. (Stamp, who could have shot his brief scenes in two days—one before and one after the old-age makeup was applied—manages to do both at once.) The direction of Christopher Cain (father of Dean, who appears in a death-scene cameo as Mormon founder Joseph Smith) is flabby, even in the massacre sequence, and the picture is shot and edited in slipshod fashion (a line of dialogue is required at one point to indicate the emigrants have been defending themselves for four days—something one would never have guessed otherwise). Indeed, all the behind-the-camera contributions are mediocre, from Juan Ruiz Anchia’s sputtering, bland cinematography to William Ross’s saccharine score.

“September Dawn,” like most “historical” pictures, has serious problems in historical terms. But in this case they’re exacerbated by the simple ineptitude of the filmmaking.