In the dark nights, where the silence eats the stars, a ruthless killer known as the X Killer returns after years of silence. He decides to hunt again. Hong Li Wei, a brilliant detective and psychiatrist, lost her little brother to the hands of the X Killer and swore to find him. Yoon Xi Yuan, a sharp detective no one dares to mess with silent, calculating, and hiding a deep secret that could turn her ordinary life into regret.