To describe When Evil Lurks as a horror film about demonic possession is to conjure images of projectile vomiting, spinning heads, tortured priests spraying profanity-spewing children with holy water, and, well, the Conjuring franchise. But Argentine writer-director Demián Rugna’s harrowing film isn’t interested in those things.
The distinction becomes quickly apparent when our protagonists, adult brothers Pedro (Ezequiel Rodríguez) and Jaime (Demián Salomon), encounter the possessed Uriel, the eldest son of an impoverished old woman (Isabel Quinteros) living on remote farmland. Uriel has become a “rotten,” a human incubator for a demon. His body has swollen to an immense size, covered in tumorous, oozing growths and incapable of being moved by a single person.
Here, possession functions like a disease that infests its surroundings. There are procedures to follow and even bureaucratic processes that are meant to respond to the disease’s spread, but there’s only a sense here of the system spinning its wheels and it all seeming for naught. Uriel’s mother, for one, notes at one point that she reported his fatal transformation a year ago.
Half the film goes by before anyone fully lays out the “rules” to follow when in proximity to a demonic presence, and When Evil Lurks is at its most inventive when leaving us to infer those rules based on the characters’ vague statements and reactions to events. It’s in everyone’s reluctance to touch Uriel, as well as the vehement opposition to simply shooting him. Pedro and Jaime leave all of their potentially tainted belongings behind when they flee, and when Pedro goes to find his estranged children, he changes out of his old clothes and burns them.

Rugna ably brings our dreadful anticipation to a fever pitch, ensuring that his eerie and gory images land with profound impact. We are, for example, left guessing as to what effect the demon may have on animals, but a pregnant woman’s fearful reaction to an apparently ordinary goat tells us all we need to know. We’re also not sure how the demon will affect a human, but we see what the woman is willing to do to herself and her husband with an axe in order to escape it. By the time the film circles back to show us what happens to an animal, the results are utterly shocking in the way that only such an entrancing and original mythology could be.
With grisly violence visited upon animals and children, When Evil Lurks spares no one from the cruelty of its world. But Rugna comes by his shocks honestly—as natural extensions of character and context that contribute to a bleak and desperate atmosphere, not least of which for how the shadow of the Covid-19 pandemic informs the characters’ behaviors. This is hardly a film full of genre-savvy characters abiding by cold logic. Rather, they’re ruled by emotion, impulse, and even denial that the spell of a rotten could possibly fall on their rural community. In depicting a world that’s grown lax toward its own protections, When Evil Lurks reaches a disturbing level of truth as it traces the fallout of human failures to their absolute extreme.
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