In the early 1930s, the mysterious death of a female university student occurred in a dormitory in Shanghai. Detective Guan Cen from the Central Police Department became acquainted with Lu Yizhen, a college student who loved detective novels, as a result of the case. This incident led them to uncover a child kidnapping case that had taken place 17 years earlier. Two years later, Lu Yizhen took part in the recruitment exam for Shanghai's first group of female police officers, with Guan Cen becoming her direct superior. Within the police department, as new cases continued to emerge, the two worked together to reopen the investigation into the child trafficking case, dispersing the fog and nightmares that had long hung over their heads.