Too often, the month of August is regarded as a fallow period for moviegoing, after the big blockbusters of the summer but before the awards contenders of the fall. But the aptly titled new movie Good One is a reminder that there are always smart, interesting films being released, if you’re willing to look beyond the obvious. As it turns out, looking beyond the obvious is something that the writer-director India Donaldson has a real knack for. In just 90 minutes, she tells a three-character story that appears simple enough on the surface, yet it’s so sharp and engrossing that you might not immediately notice the deeper story taking shape underneath.

Lily Collias plays 17-year-old Sam, who’s going backpacking in the Catskills with her father, Chris — that’s the terrific James Le Gros in a too-rare leading role. They’re supposed to be joined by Chris’ oldest friend, Matt, and his teenage son, Dylan. But Matt winds up being the only one to come along; he and Dylan’s mom are recently divorced, and Dylan isn’t taking it well.

Chris himself has been divorced for a while, and he and Sam have a pretty harmonious relationship by comparison. They seem to get along even when they’re bickering, as happens when Chris criticizes Sam’s driving.

Much of the movie consists of Sam listening quietly as Chris and Matt go on and on, reminiscing about old times yet always finding new things to grouse about. Chris, a savvy outdoorsman, can’t stop complaining about how badly Matt has overpacked for a three-day hiking trip.

While the two men rarely ask Sam how she’s doing or feeling, they seem cool enough where it counts. Chris has long been supportive of his daughter’s queer identity; she has a girlfriend whom she texts during the trip, whenever she can get a cellphone signal. Matt tells Sam that she’s wise beyond her years: Unlike all the other reckless, rebellious teenagers out there, she’s a rare “good one” in his book.

Scene by scene, however, writer-director Donaldson paints a subtler picture of the dynamics at work. At times Good One reminded me of Kelly Reichardt’s quietly perceptive 2006 drama, Old Joy, which also squeezed a lot of emotional history into a fateful camping trip.

You get the sense that Sam has traveled a bunch with her dad and Matt before, and that she’s long adjusted to her designated role. When the three of them share a motel room on their way up to the Catskills, it’s Sam who instinctively rolls out her sleeping bag, without even being asked, leaving the two beds to the men. And once they reach their campsite, it’s Sam who cooks dinner for the three of them without complaint. The dynamics are complicated. Beneath the men’s easygoing manner, there’s an unmistakable air of condescension toward Sam, a sense that their appreciation of her is more conditional than genuine.

If Sam resents them for any of this, she doesn’t show it, at least not at first. Collias gives a beautifully understated performance; with very little effort, she can register everything from wry affection to barely concealed exasperation. And Donaldson, working with the cinematographer Wilson Cameron, proves as keenly observant as her protagonist. She’s alive to the beauty of the mountains, whether it’s the sight of a majestic canyon or the sound of rushing water. Some of the movie’s slow-simmering tension arises from your uncertainty about what might be lurking nearby, whether it’s a bear in search of food or three young men they cross paths with on the hiking trail.

But Good One isn’t one of those movies in which a journey into the wilderness spirals into horror. The dangers that Donaldson introduces are of a more intimate and perhaps more insidious nature. There comes a moment in the story when everything changes, and it’s at once surprising and unsurprising, all too believable and, in the moment, perhaps a little contrived.

But that hardly matters. What matters is how Sam responds to this sudden shift, and Collias shows her unpacking that response almost in real time, and with a nearly wordless intensity. Good One has the concision of a sharply etched short story, but what happens by the end can’t be easily summed up. Sam won’t soon forget the lessons of this particular trip, and neither will we.