A performance of remarkable depth, candour and vulnerability by rising star Charlie Plummer lies at the heart of this terrifically moving fourth feature film from British writer-director Andrew Haigh. Adapted from the 2010 novel by Willy Vlautin, Lean on Pete blends timeless American myths with pin-point portrayals of modern urban hardship, as its lonely teenage lead heads east from Oregon with a horse on its last hurrah. The travails are tough but there’s an unsentimental tenderness at the centre of Haigh’s movie – a melancholic counterpoint to the grim realities of life from which our young hero flees.

Plummer plays Charley Thompson, a lanky 15-year-old (he lies about his age) who has moved home umpteen times with his single father, Ray (Travis Fimmel). With dreams of playing for the high-school football team blighted by a nomadic lifestyle, Charley has become a loner who has learned to fend for himself. Running past the Portland Meadows racetrack, he meets Steve Buscemi’s trainer, Del Montgomery, who offers him a few bucks to change a tyre and help with his horses. “Never let go of the rope,” Del tells Charley; an instruction that seems to double as a diehard life lesson.

A diffident yet attentive presence, Charley has a trusting nature and finds a kindred spirit in the eponymous quarter horse, a former short-sprint winner (“Don’t blink or you’ll miss it”). The endearingly named Lean on Pete is showing signs of age, and Del is getting ready to send him, euphemistically, “to Mexico”. “You can’t get attached to a horse,” says Bonnie (Chloë Sevigny), a jockey who has suffered her fair share of injuries, and who observes tellingly that “there’s only so many times you can fall down, right?” But when all hope seems lost, Charlie hits the trail with his one true friend, heading for Wyoming and searching for somewhere to call home.

Vlautin’s novel has been described by critics as a distant descendant of Walter Farley’s The Black Stallion, with shades of Salinger and Steinbeck. There is a quote from the latter at the start of the novel that Haigh has clearly taken to heart. “It is true that we are weak and sick and ugly and quarrelsome,” Steinbeck wrote, “but if that is all we ever were, we would millenniums ago have disappeared from the face of the Earth.” Haigh paints sympathetic portraits of all the characters; the good, the bad and the ugly. Ray may not be an ideal father, but there’s a tangible tenderness in the scenes with his son, and a sense of closeness that persists even during his frequent absences. Del is a world-weary chancer who dopes, exploits and then dumps his horses, yet there’s a gruff paternal affection in his advice to Charley to “do something else before there’s nothing else you can do”. Even Steve Zahn’s drunken drifter Silver has a child-like quality that is counterposed with a violent tinderbox temper.

After the tight focus of Weekend and 45 Years (which the director described as “companion piece” pictures), Haigh widens his canvas as Charley heads into the desert, embarking upon an American odyssey to which Danish cinematographer Magnus Nordenhof Jønck responds with lyrical grandeur. While the narrative may be read as a coming-of-age story, there’s something more elemental in Charley’s search for a beloved aunt, who comes to represent his idealised yearning for a lost family life. Crucially, Charley remains at the centre of the picture, with the oblong 1.85 frame lending a human dimension to these expansive vistas, ensuring that we don’t get distracted by the scenery, or lose sight of the true focus of the story.

Unsurprisingly, Lean on Pete is a film in which gestures are more important than words. Having declared in passing that “You won’t see me again in California”, Del shoots Charley a glance that speaks volumes about his shady past. As for Charley, he may have been schooled in Sam Shepard-style manly “truths” (“The best women have all been waitresses at some point,” Ray tells him between beers), but his voice has a lilting softness, which matches the expressiveness of his face. At times, there’s a touch of James Dean in Plummer’s plaintive delivery, along with echoes of Jon Voight’s marooned hustler in Midnight Cowboy. Having made a splash in Felix Thompson’s 2015 indie-pic King Jack, Plummer has proved a mercurial presence in films as diverse as Oren Moverman’s The Dinner andmore recently Ridley Scott’s All the Money in the World. In Lean on Pete, this rising star proves his mettle in a role for which he is simply perfect.