Hye-ja is a single mom to 27-year-old Do-joon. Her son is her raison d’être. Though an adult in years, Do-joon is naïve and dependent on his mother, and sometimes behaves in ways that are stupid or simply dangerous. He is a constant source of anxiety for everyone. One day a young girl is found dead in an abandoned building and Do-joon is accused of her murder. An inefficient lawyer and an apathetic police force that closes Do-joon’s case too quickly inspire his mother to act on her own—to act as Mother in its purest form. Summoning all her maternal instincts and trusting no one, she sets out to find a killer and prove her son’s innocence.