Tae-jo(SONG Ji-hyo) works in a prison for 15 years. Even with a husband at home, she feels something is missing in her life. One day, she finds out one of the prisoners, Mi-young, has a teenage daughter, Jun-young. Tae-jo meets Jun-young for the first time at the funeral of Mi-young's mother. Watching Jun-young sitting alone at the funeral in her school uniform, Tae-jo sees herself in her. Although Tae-jo initially does not engage in other people's life, she becomes emotionally attached to Jun-young. She understands why Jun-young feels so lost without her mother and becomes closer almost like a guardian. Meanwhile, Mi-young discovers that Tae-jo is taking care of Jun-young outside the walls. Will the daughter and mother reunite beyond the bars?