Soo In, Bok Nyeo, Pung Geum, and Mi Oh, are four female prisoners at a correctional facility have been victims of a miscarriage of justice in different cases, which later turn out to have a common thread intertwined. They team up to challenge a big conglomerate for an exact revenge. These four women forge a bond based on their common grievances and lean on each other for support. Though they are not related, they become a family of sisters.