Internal affairs takes on new meaning in this distinctively involuted Argentine thriller about a spate of gruesome decapitations in an Andes backwater. Police officer Cruz (Victor Lopez) is already on the case when his lover Francisca (Tania Casciani) becomes the next to have her head apparently chewed off, a mysterious green goo smeared on the stump. Her hollow-eyed husband David (Esteban Bigliardi) is suspect numero uno: he is found naked in the vicinity of the victims and, after later being carted off to an asylum, testifies to a strange voice in his head that whispers: “Murder me, monster.”

What does this mean? Is he mentally ill? Is he literally transforming into the monster? Director Alejandro Fadel – who has been screenwriter on many Pablo Trapero projects – is in no hurry to clear things up and seems to have no interest in conventional thriller tension or catharsis. His detectives do little detecting, preferring to reel off gnomic dialogue such as a list of different phobias. Fadel bets heavy on a kind of suggestive Lynchian illogic – as with the demonic motorcycle riders who appear for no reason in the vicinity of the killings – and shoots the unfolding quasi-investigation with a dark devotional intensity. The impassive acting style – led from the front by Lopez, with a face like a burst sandbag – keeps its own counsel.

The pace is sometimes frustrating and Fadel, near the end, is perhaps guilty of displaying too much too suddenly. Yet even when the titular critter makes its full appearance, it is bewildering: alarmingly sexualised and with implications that are not quick to be digested. Everyone in the story seems to be weighted down by this strange evil, too exhausted to combat it, even psychologically secreting it themselves. Is Fadel making some comment about the struggles of South American society or history? With a little more narrative clarity, he could give Guillermo del Toro some competition in the meaningful monster stakes.

• Released on 4 December in cinemas and on digital formats.