1979 On a rainy night in summer, in a post office in Shanghai, public funds were stolen and a girl fell in a pool of blood. Shortly after the case happened, public security officers Shangguan Jian, A Su and others rushed to the scene. The victim is Lin Qiang, a bus conductor. She was taken to the hospital and suddenly swallowed something when she woke up. The public security personnel talked to her several times, but she didn't vomit a word, which brought great difficulties to the detection work. Shangguanjian and others found an empty envelope she wrote to Xiaoxiang from Lin Qiang and a photo of Zhu Fan in Xiaoxiang's home. The scout decided to start the investigation from these two clues. Zhu Fan told the public security personnel about his relationship with Lin Qiang, his jealousy of Xiaoxiang's pursuit of Lin Qiang, and his decision to marry Lin Qiang. Xiao Xiang also told the public security personnel about his business trip from Xiamen to Shanghai, because Lin Qiang gave him a wallet stolen by his younger brother Lin Yao, the details of their acquaintance and love, and the differences on educating his younger brother. According to the materials provided by the two men, the scouts overturned the idea that the original judgment was a murder case. At this time, the reconnaissance captain learned from the blood test list of blood gloves found at the scene that the owner of the gloves was Yan Fang, a truck driver of No.2 Chemical Fertilizer Plant, who had been detained for theft in the past. Inspector Yan Feng concluded that Yan Fang left his gloves at the scene after the robbery and murder. Investigators took out photos of Xiao Xiang, Zhu Fan and Yan Fang for Lin Qiang to identify, but Lin Qiang painfully closed his eyes and said nothing. Shangguanjian learned from Xiao Xiang that Lin Qiang's argument with him about educating Lin Yao led to emotional breakdown. Could my brother have killed my sister? In the re-contact between Shangguan Jian and Lin Qiang, Lin Qiang fell into memories of the past: once, Yao Lin stole an apple from a fruit shop, and she angrily wanted to hit him, but she was soft-hearted because of her brother's crying; On another occasion, Lin Yao took out Xiao Xiang's wallet in the car. At the request of her brother, she gave up the idea of pulling him to the police station. After working, Lin Yao was threatened to gamble by hooligans as soon as he got his first month's salary. He was beaten and in debt. She gave her brother a good beating, but she put up with him because her parents died young. Slowly, Yao Lin became worse. Finally, when he went to the post office to commit a crime, Lin Qiang found that he wanted to stop it and was hurt by him. Soon, Shangguan Jian, Yan Feng and Ashushun groped, disguised as "hooligans", designed and arrested moustache and other hooligans, and then arrested Lin Yao. In the hospital, Shangguanjian told Lin Qiang that the murderer had been caught. Lin Qiang said regretfully: "The murderer was me, and I swallowed a bitter fruit." ...