Twelve years ago, several murders shocked the city. The victims were all from the bottom of society, and their bodies were all found in deserted and remote places. It is speculated that the murderer may be the same person, but because of his extreme cunning, the case was very difficult for a while. Through unremitting investigation and evidence collection, the criminal police gradually confirmed the main suspect. On the way to a meeting with his daughter Ling Ran, criminal police Ling Bin hunted down the suspect and eventually died in the line of duty. Twelve years later, Ling Bin's daughter Ling Ran (played by Yu Nan) works in the polygraph center of the technical department of the criminal police detachment. She has successfully solved several major cases using polygraph technology and has become famous. Chen Hu (played by Xing Jiadong), the leader of the serious case team of the criminal police detachment, partners with her. Although the two have different ideas in criminal investigation and solving cases, they also have a tacit understanding, and suspicious cases occur one after another...