In the 1950s after the Korean War, a gentle piper with a limp, Woo-ryong, and his sick young son, Young-nam, are en-route by foot to Seoul when they reach a remote village. Woo-ryong shows the chieftan a note written in English that he was left by an American doctor, explaining that if the piper makes it to the address in Seoul within the month, he will treat the tuberculosis-stricken Young-nam. The Chief agrees to let the pair stay for a short while, on the condition that they do not tell the rest of the village that the war has ended. Woo-ryong learns that the village is plagued by rats that do not fear humans nor fall for traps or poison. He offers to help rid the village of its infestation in return for money he can use to pay for Young-nam's treatment. Using his knowledge of herbal medicine, he creates two powders: one which will drive the rats into the open, and another to lure them into a cave which he and Young-nam seal with a boulder. He earns the village's trust and becomes smitten with the trainee shaman, Mi-sook. The Chief claims that the rats came to the village after the locals temporarily evacuated to avoid approaching Chinese soldiers. This is not the truth. Unbeknownst to Woo-ryong, the village was actually a leper colony. Fleeing the Chinese, the Chief begged the lepers and shaman to allow the villagers to stay until the war passed. However, after being given shelter, the villagers forced the lepers and the shaman into a cave. They later found the lepers killed and eaten by rats. The shaman survived and prophesied doom on the villagers and their children. In response, the Chief and villagers burnt the shaman alive: the aggressive rats then fled the cave and infested the village. Mi-sook starts to fall in love with Woo-ryong. When he tries to convince her to go with him to Seoul, the Chief is enraged. He beats Mi-sook, then convince the villagers that Woo-ryong is actually a communist spy who brought the rats with him and seduced Mi-sook. At a village meeting, the Chief uses a dead cat as evidence that Woo-ryong has not rid the village of rats, and holds up Woo-ryong's English note as proof that he is a spy; it is revealed to the audience that the note actually says nothing more than 'kiss my ass, monkey.' The villagers turn against the piper and the Chief's son Nam-soo chops off several of his fingers. As the villagers beat Woo-ryong, Mi-sook arrives with a self-inflicted stab wound. She tells them that the village's children will be at risk of death, repeating the prophecy made by the shaman, then dies. The Chief takes Woo-ryung's pipe, but lets him and Young-nam leave. However, he puts two poisoned rice-balls in Woo-ryung's knapsack. The injured piper falls asleep while his son sneaks back to the village to retrieve his father's pipe from the Chief's house. On the way back, Young-nam eats one of the poisoned rice-balls and dies in Woo-ryung's arms. Woo-ryong sets out in revenge. After burning his son's body on a funeral pyre, he covers himself in the special powder he used earlier and reopens the cave. He severs the remaining fingers on his mutilated hand to lure out the rats, then plays his flute to drive them into the village. The rats attack and eat the villagers, including the Chief. Come morning, only the village children are left alive. Woo-ryung plays his pipe and leads the unsuspecting children to the cave where he had trapped the rats. He seals the children in, and driven to despair, stares into the camera as the film ends.
The Piper received mostly positive reviews from critics, who praised the film's atmosphere, Maggie Lee from Variety praised the film's performances, cinematography, and historical/political themes. Lee concluded her review by writing, "As a bleak fable on human nature, it’s pretty old hat, but as an allegory on Korean history and politics, the movie proves cynically observant, with starkly economical storytelling and sharp visual effectsto boot." Luke Ryan Baldock from Hollywood News, rating the film four out of five stars, offered the film similar praise, writing, " It’s depressing to be sure, but very rewarding for lovers of dark cinema". Time Out awarded the film four out of five stars, writing, "Frequently arresting and blowing a breath of originality into this year’s stale crop of commercial Korean fare, Kim’s film only falters with a needlessly lengthy setup and a few inchoate sideplots. Those minor grievances aside, The Piper remains a wickedly fun gust of chills that is just the ticket to beat the heat this season." Pierce Conran of Screen Anarchy called the film "engrossing and entertaining", praising the film's characterizations, imagery, emotional resonance, and finale.
