What a tricky, twisted thriller in a minor key “Gone in the Night” turns out to be. Well-cast and toying with a tetchy, testy subtext, its virtues tend to suck the life right out of its shortcomings.

Ostensibly about an older woman (Winona Ryder) looking for the reasons her younger lover (John Gallagher Jr.) ditched her on a weekend getaway in the boondocks, it’s really about generation wars, a parable about Boomers, Gen X and those mouthy punks, Millennials.

Can’t we all just get along?

At its best, it’s a clever riff on competing values systems, lifestyles and agendas, a dance through every nasty thing this generation ever said about that one. Or that other one.

Kat and Max seem mismatched the moment we meet them. She’s a well-preserved 50ish, driving her ancient Volvo wagon into the redwoods. He’s a dozen years younger, switching up the music, prattling on about getting her out of her “comfort zone,” and in the passenger’s seat because “I don’t drive.”

But at least he talked her into this weekend rental, and she’s taken the dare.

“I will let you know when I’ve had enough adventure.”

But there’s another, younger couple already in this cabin in the woods. Al (Owen Teague) is sullen and dismissive. Greta (Brianne Rju, fierce) is everything the world tags Generation Z with — a virtue signaling, “capitalism” and “cis normal” bashing, entitled brat. Greta’s pushy and forward, figuring her youth and minority status entitle her to ageism and a lot of “OK, Boomer” judgement.

But Greta is the one to suggest the apparently double-booked newcomers just stay the night. Greta’s the one to make how-pretty-you-still-look cracks ” to Kat, “quite a catch” digs at Max’s ditziness and “that’s hot” endorsements when she hears how they met.

“I was his teacher.” OK, it was a continuing education class the plants-expert/plant shop owner was teaching on hydroponics. Max was just…interested in growing things hydroponically.

All it takes to bust this couple up is a “couples” board game that crosses a few lines, and Kat going to bed before everybody else. A weeping Al is her next morning clue that impulsive/flaky Max has run off with impulsive/predatory Greta.

The plot concerns Kat’s efforts to get over this by finding out where he/they went, tracking down Greta for answers or a confrontation or something else, she doesn’t know what.

To get those answers, she’ll have to find the renter who rented that house to two different couples the same weekend. Nicolas is played by Dermot Mulroney with a twinkle, a hint of mystery and an obvious age-appropriate interest in this cute stranger with her strange “stake out” stalking obsession over being romantically-wronged.

Casting onetime wild-child Ryder as Kat lends credibility to Kat’s rants about “I don’t need to spend another night in an abandoned warehouse with a bunch of f—–g tweakers! I’ve DONE my time!”

And it’s kind of hilarious when Kat/Ryder has to show up at just such a venue and talk her way past the doorman.

“Are your KIDS in there, or something?”

Tju, of TV’s version of “I Know What You Did Last Summer,” is gloriously mean as Greta, 20something and not cursed with burden of self-reflection but into “very intense ambient noise-core” sound. Or maybe I’m just taking Winona (and Mulroney’s) side in their claps at “20 year-olds playing Nerf darts all day” while the world burns.

“Who IS this woman? What is her DEAL? Does she even realize what she did?”

It will take that “bucket list item” first-ever stake-out, revelations through flashbacks and a not-quite-the-knockout-it-might-have-been finale to sort this mystery out.

It helps that Ryder, Tju, Gallagher, Teague and Mulroney are just as good at personifying generational foibles as they are at delivering the generation gap putdowns.

And director and co-writer Eli Horowitz, a veteran of TV’s “Homecoming,” throws in just enough curveballs to keep us guessing and just enough generational jabs to make the script kind of funny and kind of mean-spirited.

If he gets a handle on how feature films should finish — a common failing of filmmakers making the series TV to cinema leap — he’ll be one to watch.

Rating: R for language throughout and brief bloody images.

Cast: Winona Ryder, Brianne Tju, John Gallagher Jr., Owen Teague and Dermot Mulroney.

Credits: Directed by Eli Horowitz, scripted by Matthew Derby and Eli Horowitz. A Vertical release.

Running time: 1:30