In the 1950s, in the wake of the Korean War, a gentle wandering piper with a limp, Woo-ryong, Ryu Seung-ryong, travels by foot toward Seoul with his sick young son, Young-nam, Goo Seung-hyun. They arrive at a remote village where the village chief, Lee Sung-min, graciously offers them shelter at his home. The piper shows the Chief an English-written note he claims names an American doctor in Seoul who can treat Young-nam. The Chief, who asks him not to reveal that the war is over, acknowledges the request but cannot read English himself. Amid this tension, Woo-ryong grows close to a villager named Mi-sook, Chun Woo-hee, who has lost her husband and child in the fighting.
The village is plagued by rats that fear neither humans nor traps, and a grim history threads through its quiet facade. The Chief explains that they fled here when Chinese soldiers were approaching their old village, hiding the lepers in a cave with the village shaman. When the Chinese threat never materialized, they returned to the cave only to discover the lepers had died and were being eaten by vermin. With no shaman to keep them at bay, the rats overran the settlement.
To rid the village of the rats, Woo-ryong offers his services in exchange for a price that could help pay for Young-nam’s care—a cow to ease the family’s burdens. He spreads a special powder across the village and climbs to a hilltop, where a smoky fire blankets the area in dense smoke. At the same time, Mi-sook begins a purification rite with bells, having been pressed into the role of the new village shaman by the Chief. As Woo-ryong’s powder drives the rats into a cave, the vermin stream from the buildings and into the underground pass.
Mi-sook, drawn to Woo-ryong by his kindness, gradually falls for him, and even Young-nam begins to call Mi-sook “mummy.” Yet the Chief’s grip on the village tightens as he plans to keep the end of the war a secret to maintain control, and he schemes with his son, Nam-soo, Lee Joon, to deny Woo-ryong the promised reward. They sow doubt among the men, spinning the tale that Woo-ryong is a communist spy who brought the rats with him. During a village meeting, a dead cat is produced as “proof,” and the English note is seized as espionage. The note itself reads not a doctor’s name but a crude insult: the Chief holds up Woo-ryong’s note and proclaims a spy’s material, while the phrase itself is revealed to be a joke: > "Kiss my ass, monkey."
Desperation rises as the Chief tries to seize the money Woo-ryong deserves. Nam-soo carves off two of Woo-ryong’s fingers, and the villagers turn on the piper and his son. Even Mi-sook condemns them, but she reappears in a shamanic trance and prophesies doom—repeating the elder shaman’s ominous warning that on a day without sun, everyone may die, and their children might live or die. The ritual ends with Mi-sook fatally wounded, dying soon after.
Before departure, the Chief slips two poisoned rice balls into Woo-ryong’s knapsack, intending to kill the pair and keep their location a secret. Young-nam, curious and hungry, sneaks back to obtain his father’s pipe but consumes one of the poisoned treats and dies.
Driven by grief and anger, Woo-ryong prepares for revenge. He cremates his son and covers himself again with the powder that lured the rats. He reopens the cave and uses his two severed fingers as bait, then begins to play his pipe to draw the rats back toward the village. The swarming vermin descend on the adults, devouring them all, including the Chief and his son. By morning, the village is left with only its children. Woo-ryong leads the survivors to the cave and seals the rats inside, before turning his gaze toward the camera with a stark, unwavering look.
