Hye-ja is a ginseng vendor and an unlicensed acupuncturist in a small town in southern South Korea. She dotes on her son, Do-joon, who is 27, unemployed, and mentally incapacitated on some level, which Hye-ja seems to ignore.
A high school girl is found dead on the roof of an abandoned building, and the local detectives arrest Do-joon based on circumstantial evidence. They coerce him to sign a confession and quickly imprison him. Hye-ja, distraught and convinced he is innocent, searches for the real killer, uncovering many secrets from the townspeople.