“When Evil Lurks,” the Argentinian horror thriller titled “Cuando acecha la maldad” in Spanish, drops the viewer into a world where “evil” is recognized, accepted and somewhat understood.

Even if the locals in this corner of rural Argentina can’t figure out why they’re dealing with a demonic possession outbreak, as such things are mostly in “the city,” they know “rotten” when they see it, hear it and smell it. They even have “rules” for coping with it.

“Do not use electric lights” (in Spanish with English subtitles) as evil travels “in the shadows” of those. “Do not try to kill them with guns.” “Do not name” this which must not be spoken of,.

You can go to the cops, because in this corner of the world, even the police know what “a rotten” is and what its presence heralds. But they don’t know any more than you do about how to stop what’s happening.

Brothers Pedro and Jimi (Ezequiel Rodríguez and Demián Salomón) hear shots in the dark from their farm. Older and savvier Pedro even identifies the weapon, a pistol. But they don’t go and check it out in the dark. They’re not idiots.

The next day they do, and sure enough, there’s a body. Or half of one. It’s entrails are laid bare, and neither one of them reacts with revulsion, surprise or fear. But Pedro has a suspicion.

Alerting their neighbor (Luis Ziembrowski) to this and visiting a third neighbor only confirms that hunch. There’s a Jabba-bloated, puss-filled man suffering in bed as his hapless mother and sibling fret about what to do, and what not to do.

Telling the cops is standard operating procedure, but pointless. Dashing to Pedro’s ex-wife (Desirée Salgueiro) and new family to get them out of there is futile. A “rotten” has been discovered and not dealt with. The body count has already notched multiple corpses.

Writer-director Demián Rugna, of “Cursed Bastards” and one of the talents behind “Satanic Hispanics,” plops us into this world unprepared, and turns our vague unease into genuine shocks when the violence comes.

His technique is sometimes crude — jumpcuts, sped-up camera effects — because visualizing how someone might kill herself with an ax in a way that doesn’t look faked is a challenge. But it’s a largely effective piece of storytelling as the day after the first night drags onto into a hellish second night where the outbreak spreads, children are involved and an “expert” (Silvia Sabater) may or may not have the answers necessary for fighting this contagion, or even surviving the night.

Rodríguez, in a Hugh Jackman as Wolverine beard, is the driving soul of the piece, showing us a man overmatched, not quite panicking and yet rattled enough to forget the rules, ignore warnings and act on instincts that may let him down in this, the crisis above all crises.

Chilling images — children, gathered and alert at their desks in a pitch-black classroom because they’re either already possessed, or adhering to that “no electric light” dictum — are scattered, and the moments of mayhem are spread a bit thin.

But “When Evil Lurks” is still one of the most original horror films of recent memory and a pretty convincing argument to turn out the lights when you’re not using them, no matter how scary the dark is, especially out in the sticks.

Rating: unrated, graphic, grisly violence

Cast: Ezequiel Rodríguez, Luis Ziembrowski, Demián Salomón, Isabel Quinteros,
Desirée Salgueiro and Silvia Sabater

Credits: Scripted and directed by Demián Rugna. An IFC/Shudder release.

Running time: 1:39