“Gwen” has the tenor of a spooky folk Welsh folk legend and the grasping, gasping punch of an Industrial Revolution parable.

Dark, helpless, grim and bleak? It’s all a part of the windswept and gray setting of this period-perfect period piece from writer-director William McGregor.

Eleanor Worthington-Cox of “Maleficent” and “Action Point” is the title character, a Welsh teen struggling under the thumb of her mother (Maxine Peake of “Peterloo,” TV’s “Little Dorrit”) and the conditions of the day.

It’s the early 19th century. Father is “away in the fighting” and their corner of Wales is transitioning from farms to “quarries,” open-pit coal mines to fuel the steam engines that have come to rule Britannia.

Gwen keeps their sheep, tends their vegetables and dreams of the day, with her doted-on little sister (Jodie Innes) when their beloved father returns.

But Mother being a stern taskmaster isn’t enough. Strange, lethal goings-on around them soon visit their farm as well. Gwen hears sounds on the farm in the night.

Mother’s reassurance, “I’m sure there’s nothing to worry about,” isn’t reassuring at all.

As their livestock die and the woes pile up, Mother starts having seizures and Gwen tries to pick up the slack even as the helplessness of it all falls entirely on her shoulders.

McGregor is a TV director who cut his teeth on “Poldark,” “The Missing” and “One of Us/Retribution.” He’s most concerned with mood, here — foggy, gloomy hillsides, lowering skies, a girl in her nightgown wandering into the dank dark with a lamp, pleading “Who’s there?”

Britain’s eternal class wars flicker in the subtle threats and intimidation the family faces. There’s not a lot of mystery about what they’re up against — not when a sheep’s heart is found nailed to their door after the local coal baron (Mark Lewis Jones) leans on Mother to sell out, after church service.

McGregor fleshes in period detail, the ivory pin used to prick one’s finger so that blood can add a little blush to one’s cheeks, the simple, candle-lit meals, the mud, muck, life-and-death nature of farmwork and the feeble hopes that the local mine’s doctor (Kobna Holdbrook-Smith) can offer Mother some relief from what ails her.

Worthington-Cox has the pluck to pull off Gwen, and McGregor’s handling of the admittedly thin material is expert and artful — flashbacks showing that things there were always thus, but at least the family laughed and loved before Father went off to fight some rich man’s war for empire and markets.

Narrow in focus it may be, and it could certainly use a few more spooky touches to animate the “mystery” part of all this — Mother scattering sheep bones to ward off, what? Screeching animals in the night suggest The Cat of the Baskervilles might be on the prowl.

But “Gwen” is still a fascinating, immersive period piece that captures the helplessness of the working poor and the callousness of those who aren’t as aptly as, well, “Peterloo,” without getting the militia involved.

MPAA Rating: unrated, graphic violence

Cast: Eleanor Worthington-Cox, Maxine Peake, Jodie Innes, Kobna Holdbrook-Smith, Mark Lewis Jones

Credits: Written and directed by William McGregor. An RLJE release.

Running time: 1:24