A plague has pushed Argentina to the brink of collapse in this 2023 horror flick about two brothers (Ezequiel Rodríguez and Demián Salomon) who find that when society goes to hell, demonic possession is nine-tenths of the law.

Like the bisected body the brothers find in the woods, When Evil Lurks is very much a film of two halves. The first is an intense, interesting and insane thrill-ride with Western undertones, like if the Coen brothers made a Final Destination film. The second is slow and generic, as the fun of Demián Rugna’s feature is cannibalised by unnecessary exposition and supernatural waffle.

This is a shame considering the stomach-churning setup, which mines pandemic-induced anxiety for body horror and social commentary. Inspired by news stories of cancerous pesticides infecting children in Argentina, its themes of authoritative negligence, bureaucratic gaslighting and unchecked power ravaging the land are universal. The movie depicts the demented domino effect of bad decisions by those who act too late, only to then make things worse.

Those apt ideas inject purpose into the pus, revelling in Raimi-meets-Romero madness. One of the rules is that shooting “the Rotten” causes the plague to spread, but try telling the characters that; one farmer is so wedded to his gun that he is willing to infect his unborn baby in order to protect his land.

But these political elements soon fall off the bone, leaving disappointingly little to chew on. The movie peaks in the middle when our panicked protagonist goes to retrieve his kids from his ex-wife (Virginia Garófalo), in a sequence so funny, brutal and surprising it leaves little room for escalation. Instead Rugna takes his foot off the gas, introducing a purely expository character (and an misguided autism plot point) that muddies rather than clarifies the epidermic epidemic.

At that point When Evil Lurks decomposes from something lean, mean and free of bullshit into folk horror nonsense. But at its best, the power of blight compels you.