Revenge is a subject that’s ubiquitous in Westerns, but writer-director Jared Moshe gives it an unusual spin in “The Ballad of Lefty Brown,” making the hero intent on getting the villain not some stalwart, stoic figure out of a Sergio Leone epic but the crotchety old sidekick who might have been played by Walter Brennan or Gabby Hayes in one of the Hollywood pictures that inspired Leone’s spaghetti homages. Bill Pullman might not be the first person one might think of to embody such a character, but in the event he pulls it off nicely.

Lefty Brown is the long-time right-hand man of Eddie Johnson (Peter Fonda), a legendary lawman who’s hung up his badge to become a Montana rancher. His fame has led to his selection as the first senator of the state (which was admitted to the union in 1889), and he and his wife Laura (Kathy Baker) are preparing for the move to Washington. They’re also arguing about his decision to leave Lefty in charge of the spread while they’re in the East; she doesn’t think he’s up to the job.

In the middle of their conversation, one of the hands rides in to announce that three of their horses have been stolen by rustlers, and Eddie and Lefty saddle up to track them down. They’re ambushed, however, leaving Eddie dead and Lucky vowing to find the killer and—presumably—mete out the summary justice that Eddie, as we have witnessed in a prologue, was accustomed to administer. After he departs, there arrive two old friends who used to ride with Eddie—James Bierce (Jim Caviezel), now Montana’s first governor, and Tom Hannah (Tommy Flanagan), a marshal who was once a heavy drinker but is now off the stuff. While Bierce remains with Laura, Hannah rides off to find Lefty and bring him back before he gets himself killed.

Lefty, however, has bumped into a young drifter, Jeremiah (Diego Josef), an aficionado of cheap novels about gunslingers, and effectively assigns himself the role of sidekick to the elderly galoot. Hannah eventually catches up with them and reluctantly joins the search, which culminates in a showdown with the rustlers and the capture of the killer, Frank (Joe Anderson). But that’s only the half-way point in a narrative that includes, among other things, Lefty being wrongly accused of Eddie’s murder and nearly hanged. The other two members of his posse face some rough times as well, while there turns out to be a lot more behind Eddie’s death than the theft of a few horses. Another dose of summary justice will be forthcoming as Lefty’s mission is successfully completed.

There’s plenty of familiar (indeed, overfamiliar) subtext at work here—the preponderance of legend over fact, the propensity for so-called progress to trample old-fashioned principle—but the movie’s emphasis is really on character, and particularly, as the title indicates, on Lefty, the sort of rambling old fellow who was always on the periphery in Hollywood Westerns. Taking center stage, he hardly presents a typically heroic image, being more prone to get himself into scrapes than rescue others from them. But despite his own doubts he proves indefatigable in his determination to see that his friend is avenged, and he’s loyal to others who deserve it as well, while being unforgiving to those who have betrayed his trust.

Pullman, looking older than his years, captures the man’s essential decency as well as his slightly goofy sense of mission. The role could have been played as mere caricature, but while it practically invites him to go over-the-top, he resists the impulse, and the film is all the better for it. In his hands Lefty is a bit of a stumblebum, but he’s honest and, in a pinch, capable of surprising you. The rest of the cast defer to him; Caviezel and Bates do so with understatement, while Fonda allows his semi-iconic status to take care of business; Flanagan and Josef have greater opportunity to shine and both, especially the latter, acquit themselves well.

Moshe clearly revels in the Western milieu, and serves up the traditional ambience nicely on a modest budget. Working with production designer Eve McCarney and costumer Jonny Pray, he creates a convincing sense of time and place, and with cinematographer David McFarland and editor Terel Gibson he fashions some striking widescreen images of the Montana landscape while keeping to a tempo that moseys but doesn’t drag. Nor does H. Scott Salinas’ score overdo the usual musical conventions.

“The Ballad of Lefty Brown,” like its titular sidekick, will probably play second fiddle to more inflated, portentous Westerns. But while a minor contribution to the Western genre, it offers a clever twist on its tropes.