The Piper is a 2015 South Korean period horror-thriller film inspired by the Pied Piper of Hamelin legend. It is written and directed by Kim Gwang-tae in his directorial debut.
In the 1950s, after the Korean War, a gentle wandering piper with a limp, Woo-ryong, and his sick young son, Young-nam, are en-route by foot to Seoul through the central Korean highlands when they reach a remote village. The village chief allows Woo-ryong and his son to stay at his house. The Piper shows the Chief an English-written note that he says is the name of an American doctor at a hospital in Seoul who can treat Young-nam. The Chief, who tells the Piper not to tell anyone else the war is over, agrees but he cannot read English either. Woo-ryong is smitten by a villager called Mi-sook, who lost her husband and child in the war.
Woo-ryong quickly sees that the village is plagued by rats that do not fear humans and do not fall for traps and poisons. The Chief explains he and his people came here when they heard Chinese soldiers were approaching their old village. They hid the village lepers in a cave with the village shaman. But when the Chinese had not reached the village, they returned to the cave but found all the lepers were dead and eaten by rats. The vicious vermin then invaded the village because it had no shaman to keep them out.
Woo-ryong volunteers to get rid of the rats in exchange for a pig's price that will help pay for his son's medical treatment. He spreads a special powder across the village and goes to a nearby hilltop. Checking the wind direction, he lights a very smokey fire that smothers the village in smoke. At the same time, Mi-sook, who the Chief has forced to become the new village shaman, begins a purification ritual with bells. Rats start pouring out of the buildings following Woo-ryung's powder to a cave.
Mi-sook starts to fall in love with Woo-ryung due to his kind nature. The son even begins to call her "mummy". However, the Chief threatens her if she plans to leave the village. He also plots with his son, Nam-soo, to not reward the Piper for getting rid of the rats. First, they create doubt in the male villagers' mind, making them believe that Woo-ryong is a communist spy who brought the rats with him. At a village meeting, the Chief says he will pay the Piper, but a dead cat is found. Proof the Chief says that the rats are back. He holds up Woo-ryung's English note and says it's spying material; it simply reads "Kiss my ass, monkey" - no American doctor's name, just a cruel joke. Woo-ryung reaches for the money, but Nam-soo chops off two of his fingers with a knife. The villagers turn on Woo-ryung and Young-nam; even Mi-sook condemns them. But as the villagers get ready to throw them out, Mi-sook returns in a shamanic trance but stabbed in the stomach. She tells the villagers that they will all die on a day without sun, and their children might live or die, repeating the original shaman's prophecy before she was locked up and burnt alive by the villagers. Mi-sook then dies from her wounds.
Before they leave, the Chief 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 ate one of the poisoned rice balls and dies.
Woo-ryong sets out on revenge. After burning his son's body on a funeral pyre, he covers himself in the special powder he used earlier to attract the rats and reopens the cave. He uses his two severed fingers as bait and starts playing his pipe to lead the rats back to the village, where they devour all the adults, including the Chief and his son. The following day only the villagers' children are alive, Woo-ryung plays his pipe and leads them to the cave where he trapped the rats. After sealing them all in, he turns and looks hard into the camera.