The male and female protagonists became connected because of an old case in the south of the city. During the investigation, they uncovered a secret from the fog, and thus developed a love. In the end, the truth was revealed to the world, and the two formed a beautiful marriage. Twelve years ago, there were three cases recorded on the day of the summer solstice in Jincheng. In the first case, Mr. Li Jiashan drove out late at night and never returned. The next day, the carriage was found parked outside the city gate. The horse was not tied to the carriage and the carriage was empty. People are missing. The family reported the crime, but the search failed, but he was rumored to be a murderer. Unable to bear the advice, Mrs. Li committed suicide by swallowing gold. The third uncle of the Li family raised the orphan girl Li Yi. In the second case, the loving couple named Fu died at home. The murderer is unknown. The orphan Fu Pei was adopted by the Fang family. The third case was nothing important. The first brothel, Yimeng Pavilion, reported that a thief broke in and the person was frightened. No important things were stolen, but some guests' clothes were missing. What is the connection behind the three old cases in Chengnan? What's the secret?