A serial disappearance case fifteen years ago was sealed, and the only clue was an old notebook called a "cold case book." Retired psychological portraitist Shen Zhiyao was forcibly recalled and joined forces with the new team leader Jiang Xubai to restart the investigation. Forensic doctor Bai Lu's poison analysis, archivist Zhou Yanqiu's mysterious files, and aphasic girl Lin Yuan's silent guidance revealed the silent conspiracy of the top police officers layer by layer. When the last page of the cold case book points to Jiang Xubai's father, Shen Zhiyao must choose: destroy the truth, or let all the buried scars see the light of day.
Shen Zhiyao returned to the police force and brought out the dusty cold case book. The clues pointed directly to three missing children cases fifteen years ago and a police officer who committed suicide. Jiang Xubai took the opportunity to investigate his father's death, but found in the file that his father had marked "blue iris is the key", and it was exactly that kind of flower that Lin Yuan placed every day. Bai Lu detected that all the deceased people contained the same kind of industrial sedatives, which were only used in internal laboratories; Huo Yan risked his life to steal a burned call record and pointed it at the current criminal investigation consultant. The plot of the Internet writer Zhou Yanqiu secretly protected actually matched the undisclosed crime scene - he was the real eyewitness of the year, and his identity was erased. As Shen Zhiyao gradually regained her memory, she realized that her 'misjudgment' back then was a trap deliberately guided by someone. During the investigation, Jiang Xubai discovered that a key engraved with 'C-7' was hidden in his father's belongings, and on the inside of the cover of the cold case book, there was the handwriting of Shen Zhiyao's mother: 'Don't trust anyone, including your own memory. ' When Lin Yuan wrote 'They are still looking for her' on paper for the first time, all the cold cases really started to breathe.
