In order to find the murderer of his friend, Charlier came to Xiangwan City where the murderer left clues. Before leaving, his father told him that he must seek help from the famous detective police officer Qiao Jun in the evening market. However, after Xia Lier got to know him, he realized that the so-called detective police officer was just an idle title, and Qiao Jun did not even understand the most basic knowledge of investigating crimes. Although he didn't want this confused detective policeman to interfere in his own affairs, his father asked him to do it, and his uncle insisted on Qiao Jun taking care of him. In desperation, Charlie had to stay at Qiao Jun's house. Subsequently, a series of cases occurred one after another with the appearance of the mysterious man. At the end of each case, Charlier will receive a small blood name tag, and the name tag is a different letter every time... What is the connection between the mysterious person and the blood name tag and the murder of his friend...