Indie thriller nails the male-female dynamic before stumbling over the finish line.

Very little happens in the first half of the indie thriller “Blue Jay.” And boy, is that a beautiful thing.

The tale of two hikers who meet some unsavory types on Mount Whitney offers the kind of detail many thrillers lack.

It’s spare storytelling 101. And you can’t look away.

“Blue Jay’s” second half has its moments, but it can’t measure up to the sly setup. It’s still an engaging tale, particularly if you discover it at its current home on Amazon Prime.

Sara Lindsey and Travis Aaron Wade play a new couple ready to test their courtship. They aren’t boyfriend/girlfriend yet, but that might happen by the end of their first big trip.

They’ve decided to hike Mount Whitney, the highest summit in the contiguous United States. They have all the tools necessary for the trip. It’s not that simple.

Ashley isn’t sure she’s ready for it, both the hike and her budding relationship. Jack is there to catch her should she fall (choose your meaning). Their dynamic is atypical for a thriller like this. Normally, we’re treated to a lovey dovey couple who get the shock of their lives.

Here, Jack is brusque and paternal. He means well, but you can feel Ashley’s uncertainty at his manner. And yet she’s charmed by his attentions, even if it means hiking in brutally cold weather to enjoy them.

There’s something decidedly alpha male about Jack, yet he craves a woman equally strong and bold.

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Of course they won’t be alone for long. Four fellow hikers cross their paths. The vibe is decidedly off during that first encounter, and it only gets worse from there.

James Landry Hébert (“Taken”) is the most mesmerizing of the four men. He’s cagey and charismatic, and his introduction suggests the story will be going in dangerous directions.

It does, just as the trailer portends. What’s missing is the sense of integrity that inhabits the film’s early sequences.

Lindsey and Wade are terrific as the fledgling couple. A series of flashbacks suggests the innocent of their trip’s origin. Yet it becomes increasingly frightening when drawn into a new, more disturbing context.

Fast Fact: Sara Lindsey’s first time on stage came at the age of six. She signed ‘I Love You’ to a fellow first grader in an adaptation of Shel Silverstein’s “A Light in the Attic.”

Director/co-screenwriter Michael Ciulla trots out some sketchy tics to heighten the fear. The flashbacks increase with diminishing results. A sequence involving a Go-Pro-style vantage point only illuminates the hands steering the plot.

And then there’s that ending. It’s a head scratcher on the surface. Those who snap the story pieces into place may still come away disenchanted.

The cinematography is flat-out beautiful, though, often in that casual way that adds to the naturalistic approach. And the way Ciulla sculpts the tension is fresh and raw. It’s impossible not to care about the couple’s fate. That means Ciulla and co. have more than done their jobs.

Most thrillers showcase victims who don’t necessarily choose the best path. Action heroes like Jason Bourne always knows what button to press or which door to open. The rest of us just go on instinct, and the results speak for themselves. That’s true here, but Ashley’s choices are occasionally maddening, and not in a way that enriches the story.

And those mountain men types don’t make much sense, either. A more durable screenplay would have teased out their backstory just enough to heighten the scares.

To be fair, this foursome is pretty scary as is.

Lindsey, who co-wrote the screenplay, proves the kind of heroine feminists should cheer. Ashley stands her ground but is open to new ideas. She doesn’t have an answer for everything yet will improvise as needed.

If only she suggested some other way to get to know her new beau.

HiT or Miss: “Blue Jay” stumbles during its third act, but until then it’s a solid entry in the man vs. nature … vs. man sub-sub genre.