Five years ago, on a thunderstorm night, Hong Ying, who was returning home at night, witnessed the murder of his uncle, Hong Wenyuan, the young minister of Dali Temple. In a daze, he saw the figure of the murderer. However, due to the murderer's calculations, some key memories were lost. Therefore, he was suspected by Gu Xicheng, Hong Wenyuan's apprentice, and faced him tit for tat for five years.
Five years later, while Hong and Gu were secretly investigating the truth about Hong Wenyuan's murder, they were fighting overtly and covertly to investigate two important cases that occurred in Shuntian Mansion. Just when the contest between the two was in full swing, Liu Qingmei, the madam of Wanhua Tower, was killed. The murderer left a brocade bag on her body, which contained a cork. Hong Ying was shocked to realize that five years ago, he had picked up the same kit at the scene of his uncle's death, except that his uncle's kit contained a hairpin. The murderer of his uncle committed another crime, adding a missing clue to the unsolved case five years ago. Hong Ying vowed to seize this clue and find out the truth.
But the mystery was strange. When he followed the clues and found the suspected murderer of Liu Qingmei, the headless body suddenly appeared by the lake had the ghost's life-seeking bag again. And the identity of the headless body was suspected to be the murderer of Liu Qingmei they had been looking for?
Tips were found on both deceased persons, and Hong Ying, who was carrying a secret, behaved abnormally during the investigation, making Gu Xicheng aware of Hong Ying's concealment. After some dealings, Hong Ying told Gu Xicheng the secret of the kit. The two decided to put aside their prejudices for the time being and join forces to investigate the case.
While the happy enemies were investigating the case and talking to each other, they gradually saw clearly the softness hidden under the coldness and the sincerity disguised under the dissoluteness. As the dead appear one after another, the same kit appears at the crime scene. Each kit contains mysterious objects and unknown secrets - the young minister of Dali Temple, the madam, the drunkard, the shopkeeper, the good man, and the number one scholar. What is the connection between the deceased with different identities? What was the purpose of the murderer leaving the tips at the crime scene?
The two work together to investigate the case, and the truth gradually emerges in the fog. The collection of clues pointed to a fire that occurred in the suburbs of Jiangning County fifteen years ago, and the murderer who was hiding in the fog and guiding the two people with a tips bag was hiding beside them.
After the truth came to light, Hong Ying and the unexpected murderer stood at the scene of Hong Wenyuan's crime five years ago. Everything returned to the starting point, and Hong Ying finally remembered the forgotten memory of that day. It turned out that five years ago, he saw the murderer. But time has passed, and in the process of investigating the Li Jin case, Hong Ying lost his best friend, gained his true love, and discovered the truth - "The human heart" is the most difficult mystery in the world.
Concept: The most difficult mystery in the world is the human heart