Local rumour is it's all the doing of an elderly Japanese man who moved in to the area and is said to have done all manner of bad things including sexual assault and attacking a local shopkeeper.
Incredulous, Jong-Goo goes to visit the newcomer who lives way up in the hills.
No good will come of this.
This is Korea does folk horror without telegraphing what's going on or sticking to a single playbook.
It starts out like a Police comedy drama with the protagonists ribbing each other for being fat lazy and useless, toys with cannibal cultist in the woods imagery, some zombie infection outbreak elements and settles in for the long haul with a clash of shamanic magic fighting for the souls of the villagers.
I use the words long haul as at 2.5 hours long it really does dabble in three genres as the story unfolds. Director Na Hong-jin holds this together well and uses it to good effect to increase tension throughout. The Jong-goo of the final scenes is almost like a different person from the cheerful shlubby local policeman he begins as.
A slightly bullshit ending I don't buy is the only thing that causes me to hold back a wholehearted recommendation 7/10.