In Tingzhou City, Su Wanzhou holds a copper-wrapped abacus, managing the declining Lu family's medicine shop and keeping her husband, Lu Chengan, in line, earning her the title 'Iron Abacus Lady.' Lu Chengan brings back Mianniang, who is pregnant, and insists on taking her as a concubine. Su Wanzhou does not cry or make a fuss; publicly smashing the abacus that has accompanied her for three years, she outwardly handles the concubine arrangements. Everyone thinks she has compromised, but only Lu Mingzhu knows her heart is already dead. According to their pre-marital agreement, she uses the concubinage to obtain her divorce papers. After enduring scheming in the inner courtyard, Su Wanzhou resolutely leaves the Lu family. Lu Chengan awakens to his regrets, but it is too late, and Lu Mingzhu takes over the medicine shop. Far away in Quanzhou, Su Wanzhou steps out of her pain, meets a good man who cherishes her, and reaps a fulfilling life.