The female policewoman Ran Dongdong of Xijiang City shot and killed the hostage-hidden criminal in the small supermarket on Miaoqian Street. Although he was praised, he still had a great impact on Ran Dongdong who shot the real person for the first time. When she returned home, her husband Mudafu had some questions about her shooting of the criminal, which aroused Ran Dongdong's disgust. A murder case occurred in Xijiang City. A fisherman found a female corpse by the river. The police team began to investigate the identity of the victim and named the case "Big Cave Case".

Shao Tianwei returned to the police station after investigating the situation on the night of Mudafu's incident. Mudafu went to the hospital to visit Mu's father that day, and sat on the stool of the hospital and got his pants dirty, but he could not explain why Mudafu came home at midnight, which aroused Ran Dongdong's suspicion. Ran Dongdong and Mudafu visited Mu's father and mother, and found out that Mudafu visited Mudafu that day because Mudafu was admitted to the hospital after being cheated online. Mudafu borrowed 200,000 yuan from female writer Bei Zhen to solve the problem. Mudafu explained the whole story to Ran Dongdong.

Thirteen years ago, Mudafu met Ran Dongdong under the introduction of Ran Bumo. The two fell in love at first sight and got along happily. The two even openly discussed Fang Xiaoyu, a female student who admired Mudafu. Finally, Ran Dongdong asked Fang Xiaoyu to give Mudafu a hundred days of flowers and gave Mudafu to her. Fang Xiaoyu did not persist, and the two got along happily in their marriage. Now thirteen years later, both of them feel that each other has changed. Mudafu feels that Ran Dongdong is no longer gentle, and Ran Dongdong feels that Mudafu is no longer honest.

Wu Wenchao continued to tell Ran Dongdong and Shao Tianwei about Xia Bingqing that he knew. After accepting Xu Shanchuan's money, Xia Bingqing brought the fruit knife from his family into the house that Xu Shanchuan rented for her. Xu Shanchuan gave Xia Bingqing a job contract for her parents to show rationalization. She suddenly had a lot of money. Xia Bingqing accepted all this and the conditions for being Xu Shanchuan's lover. Ran Dongdong still had many questions while listening to her story. Wu Wenchao said that Xia Bingqing had never told Wu Wenchao who was the one who raped her.

After searching for Wu Wenchao, Shen Xiaoying's attitude towards marriage in Wu Wenchao's description aroused Ran Dongdong's curiosity. After get off work, she went to Lianhu Hotel for massage and checked the scheduling records of the massage technician, and continued to investigate her suspicion about Mudafu. She found that Mudafu had not come to the door during the two check-in hours. When she returned home, she asked Mudafu that he still didn't want to say what he did in those two times. Ran Dongdong suspected that Mudafu was dating Bei Zhen, but there was no definite answer.

Wu Wenchao planned to implement the plan on Xu Shanchuan's birthday, and Xia Bingqing was ready to jump off the building with Xu Shanchuan that day to disguise himself as an accident. Wu Wenchao did not want to sacrifice two lives, so he gave Xia Bingqing another solution. On the night of her birthday, Xia Bingqing asked Xu Shanchuan to celebrate together. She planned a big show in a five-star hotel to pretend that she had a new boyfriend and wanted to break up with Xu Shanchuan, which made Xu Shanchuan, who was tired of Xia Bingqing, feel a little relaxed and mixed with reluctance

Ran Dongdong heard Xu Shanchuan's testimony inconsistently, and said that Xia Bingqing was simple and dedicated, and said that Xia Bingqing took the initiative to seduce. Ran Dongdong moved him to Xu Shanchuan with love and listened to the testimony of Xia’s father and mother, telling that Xia Bingqing told her parents that she was Xu Shanchuan’s mistress that day, the whole family hugged her head and cried bitterly. Xu Shanchuan admitted that the first time Xia Bingqing had sex with him was forced by him. The investigation of the case has achieved phased results. Ran Dongdong asked Mudafu to celebrate together, but when the two met, they inevitably brought up suspicion of Mudafu's cheating.

Ran Dongdong went to his parents' home and told his parents that he was going to divorce. Seeing that his parents were two people who didn't love each other but could barely make do with each other, they were even more sure of their divorce. They also found a lawyer to find Mudafu. Mudafu said that they wanted to talk to him by themselves. Ran Dongdong's cold attitude when discussing the divorce conditions made Mudafu very hurt. Mudafu asked to file a divorce after the big trap case was solved. Ran Dongdong is no longer responsible for the big pit case, but he is still investigating and surveillance himself, discussing the case with Mudafu.

The police team continued to pursue Wu Wenchao's whereabouts, and found his traces in the unfinished building but still did not catch him. The police found that Wu Wenchao's mobile phone signal appeared in Zhinan City, the Sino-Vietnam border. In fact, Wu Wenchao sent his mobile phone to his local classmate Fang Ziming. After reasoning, the police believed that Wu Wenchao should be returning to his hometown, so they were preparing to go to Xinglong County to investigate. During the investigation, Shao Tianwei told Ran Dongdong that Mudafu had asked him for something. Ran Dongdong also said that he had not cut his wrists, because Mudafu had hallucinations.

After Wu Wenchao was detained, he confessed to another part of the big pit case, saying that Xu Haitao gave him 500,000 yuan and asked him to plan to make Xia Bingqing disappear. Xu Haitao said that he just wanted Xia Bingqing to stop harassing Xu Shanchuan, and did not ask him to use violence. It was not Xu Shanchuan's instructions, but he wanted to help him solve this problem in order to be grateful to Xu Shanchuan for buying a house for him. After Xia Bingqing's death, Wu Wenchao asked Xu Haitao for the final payment and wanted to leave the city, but he said that he did not kill Xia Bingqing and did not know who killed it.

Ran Dongdong and Mudafu have not completed the divorce process and are still in crisis. At this time, Bei Zhen invites Mudafu to meet, and Mudafu is in trouble. On the other side, Ran Dongdong continued to investigate the big pit case and found that Liu Qing had cancelled all information about the city and went to Wuzhishan to defect to his ex-girlfriend Bu Zhilan. The police team immediately went to Wuzhishan. Liu Qing said that the immigration procedures were actually completed, and Xia Bingqing regretted it. He also lied to Wu Wenchao to elope with Xia Bingqing, but he was afraid that Wu Wenchao would ask him to refund the money.

Ran Dongdong and Mudafu went to the psychiatric department to clarify Ran Dongdong's distrust of Mudafu. He discussed love with Mudafu at home and recalled his first love. All of this only existed in Ran Dongdong's mind and was not real. The double pressure of the case and family made Ran Dongdong suffer. Mudafu completed the project, and Ran Dongdong agreed to celebrate with him. The two came to their new house. Mudafu, who thought it was a two-person world, found that Ran Dongdong had made both families come over to let Mudafu move here to live.

After talking to Bu Zhilan, Liu Qing came to see Ran Dongdong, saying that he had not killed anyone and began to confess the truth. A year ago, Liu Qing was applying for an immigration to Xia Bingqing, and met a decoration worker named Yi Chunyang. They worked near Liu Qing's company and became familiar with each other. Yi Chunyang also showed Liu Qing's poems he wrote. Because he could not complete the plan to immigrate Xia Bingqing, Liu Qing was about to escape. On the day he returned to the company to pick up things, he met Yi Chunyang again.