A family annihilation puts Lu Chen on the road to pursue the murderer.
An unsolved case leads to a shocking conspiracy spanning eighteen years.
Murders occur on rainy nights, girls disappear, old cases reappear, and organizations emerge.
Criminal police, forensic doctors, hackers, the iron triangle enters the game.
There is a mole in the police station, a wealthy family hides a culprit, and the killer is everywhere.
All clues point to the same secret: Unsolved Case No. 731.
