It happens often enough that it’s worth pointing out this neat bit of role-reversal in “The Unfamiliar.” Our heroine, Izzy Cormack, turns to her husband Ethan and says, “Stay here and call the police.” Or “Wait here, I’ll find” Emma or Tommy or Lily, whichever of their children is missing, taken by demonic spirits.

Izzy, played by Jemima West, is not just the protagonist here. She’s “wearing the pants” as we used to say — fixing their busted Mercedes, taking charge in a crisis, fighting back at whatever’s attacking her and her family, even if it’s all in her head.

Because Izzy is a British Army doctor, fresh back from Afghanistan. PTSD is very much on her mind as things go “bump,” her son Tommy (Harry McMillan-Hunt), husband (Christopher Dane) and teenage daughter (Rebecca Hanssen) act strange and all ANYbody can ask her is “Did you take your pills?”

The movie around this take-charge heroine is rubbish, with Hawaiian “spirits” stirring up stuff in a plot straight out of “The Brady Bunch.” There’s rarely a chill and only a scene or two in the third act that get across any sense of peril.

And you have to take off some of the points you give the script for making a woman the center of the action for laugh-out-loud moments of cultural appropriation. But aside from that…

Izzy comes home from a combat tour to a family that seems a little wrapped up in college-professor-husband Ethan’s latest project, either a non-fiction book on the Tiki gods and spirits of Hawaii, or “a children’s book,” complete with horrific illustrations, that uses those gods and monsters in a kid-friendly story.

Teen Emma (Hanssen) is still studying piano, but kind of remote. Son Tommy (McMillan-Hunt) is precociously tinkering with a short wave radio of his own design.

But the static out of that radio is sinister, Tommy keeps insisting he uses it to “talk to Dad when he’s asleep.”

Pictures fly off the walls, and Izzy is hallucinating deathly injuries her children incur. We see her visit a shrink, but don’t go into the session. Because there’s a fellow (Ben Lee) in the waiting room who seems to know her, reassures her that she’s “not mad,” and well, he has a BUSINESS card.

Why not bring him and his partner in for a seance?

Izzy’s efforts to “get to the bottom of this” include CCTV cameras, even though everybody knows demons don’t show up in HD. Ethan’s solution is a family holiday, back to Hawaii where his “research” began.

West never takes Izzy off the deep end — she is ENGLISH, after all. It’s a performance that shows us curiosity and concern, and the odd moment of shock. But Izzy isn’t given to panic, weeping or unalloyed terror.

That’s a justifiable approach to the character, but one that robs the movie of pathos and urgency. Because nobody else picks up the scream-in-fright slack.

What is the DEAL with these kids, this husband? So unconcerned. That mystery drives the story, and frankly isn’t enough to force the viewer engage with it.

The whole affair, with its posh accents, country house in England and absurdly roomie “jungle” rental in Hawaii, is entirely too prissy to scare anybody.

And the one good action beat — SOMEbody is allergic to bees, and is thus tormented by them by the demon — comes too late to make any difference.

MPAA Rating: Unrated, graphic violence, much of it involving children.

Cast: Jemima West, Christopher Dane, Harry McMillan-Hunt, Rachel Lin and Rebecca Hanssen.

Credits: Directed by Henk Pretorius, script by Henk Pretorius, Jennifer Nicole Stang. A Dark Star release.

Running time: 1:29