A married couple with children prepares for divorce after 40 years of living together. The father does not agree to the divorce, and his three daughters, Gwang Nam, Gwang Sik, and Gwang Tae, don't understand why. The mother, who has lived through many challenges, is murdered while processing the divorce. All the family members, including the father and the Revolutionary Sisters, become suspects. On top of that, a romantic conflict sparks between the sisters. Will the father and the Revolutionary Sisters be safe? Who could be the murderer among them?