When I would begin to describe the basic stanchions of “Lean on Pete” to friends and colleagues over the last few weeks, I could see them struggling not to roll their eyes.

And most of these conversations were via text and emails.

When I would tell people about this beautifully rendered film about a boy on his own in a tough world and the aging horse he comes to love …

Wait! Hang on. Trust me: “Lean on Pete” is not some 1962-ish, Technicolor kid’s movie about an apple-cheeked boy and his beloved horse and Gosh Pa, isn’t Pete just the best horse and don’t you wish he could live forever?

This is not that movie.

This is more like a Gus Van Sant road trip influenced slightly by “The Grapes of Wrath.”

Granted, writer-director Andrew Haigh’s elegiac, gorgeously photographed and sometimes almost fantastical journey indeed has some of the characteristics of a sunny and sweet film about a boy who finds something special in a horse on the cusp of outliving his usefulness. But as the film takes deeper and darker turns, it also becomes something special, something unflinchingly honest, something that will punch you in the gut AND touch your heart.

Charlie Plummer, so good last as the kidnapped John Paul Getty III in last year’s “All the Money in the World,” is asked to carry this film (with the invaluable help of some of some first-rate supporting players), and he delivers brilliant work.

Plummer plays Charley, a 15-year-old kid who has just moved to a small and rundown house in Portland, Oregon, with his father Ray (Travis Fimmel, excellent), because there was a job there for Ray. (Charley’s mother has been out of the picture for a very long time.)

Ray’s been getting by on looks and bad-boy charm pretty much forever. He’s one of those guys who always seem to owe three buddies money, two women an apology and one boss an explanation. (And usually with a can of beer in his hand.) Ray isn’t a bad parent; he loves his son. It’s just that he can barely take care of himself, let alone a shy, whip-smart, slightly quirky high schooler.

Ray and Charley have arrived in town during summer break, so Charley has a lot of time on his hands. He goes for long runs nearly every morning, and on one such excursion he passes by a racetrack, where a crusty owner-trainer named Del (Steve Buscemi) offers Charley a few bucks if Charley can help him out with a chore. This leads to Del hiring Charley as a stablehand, tasked with grooming and exercising and feeding and watering the horses — and of course cleaning out their stalls.

Del does not train elite thoroughbreds. He has a small stable of low-level quarter horses — sprinters that race a quarter-mile or less. He travels the Northwest with one or two of his horses, racing them at fairgrounds and dilapidated tracks and “courses” that look like someone just plowed a straight path on the farm.

Buscemi provides the occasional moment of comic relief — as when Del is appalled by how fast the teenage Charley scarfs down his food — but Del is no gruff-but-warm father figure. He’s a hardened, world-weary, washed-up scrapper who has long ago stopped thinking of his horses as anything but commodities, to be rode hard and long until they’re a liability, at which point he arranges for them to be sent away, for good.

When Charley takes a liking to Pete, a game but aging competitor, Del warns him: “Don’t treat him like a pet! They’re not pets.”

Chloe Sevigny is Bonnie, a veteran jockey who grows fond of Charley but issues the same warning about not getting attached, especially after Charley finds himself with nowhere to go and starts living in the stables, right next to Pete (unbeknownst to Del).

Forget it, Del and Bonnie. Charley sees in Pete a chance to take care of someone in a manner in which he’s never been taken care of.

Charley’s bond with Pete and his despair at his own situation leads him to take drastic measures and puts him on a path in which he has memorable encounters with an unstable charmer who’s been living on the streets for years; two veterans just home from seeing combat overseas; a girl about his age who endures terrible abuse from her grandfather, and a kindly waitress in a diner, among others.

Not everyone is sympathetic to Charley’s plight — and there are times when Charley’s actions, while understandable, are seriously illegal and in one case shockingly brutal.

Still. All this kid really wants is a “regular” teenager’s life.

One of Charley’s fondest memories dates back prior to the move to Portland, when one of his football teammates invited him over for dinner. His friend lived in a very nice house, and the whole family was welcoming and warm and laughing and having a great time around the dinner table. Charley figures they probably don’t even remember him, but he sure remembers that day, and he’d sure like to have another day like that again.

It’s hard to imagine anyone watching “Lean on Pete” and not rooting hard for Charley’s wish to come true.

★★★★

A24 presents a film written and directed by Andrew Haigh, based on the novel by Willy Vlautin. Rated R (for language and brief violence). Running time: 121 minutes. Opens Friday at Landmark Century Centre and CineArts 6 Evanston.