A couple with children prepare for divorce after 40 years of living together. The father does not agree with the divorce, and his three daughters, Gwang Nam, Gwang Sik and Gwang Tae, do not understand why. The mother, who has gone through many trials, is murdered while filing for divorce. All members of the family, including the father and the Revolutionary Sisters, become suspicious. In addition, a romantic conflict arises between the sisters. Will the father and the Revolutionary Sisters be safe? Who could be the killer among them?