Han Qing (played by Sun Li), a female police officer of the Sanhe Criminal Investigation Team, secretly continues to investigate the whereabouts of Zhong Wei (played by Luo Jin), her tacit partner who has worked with her for many years, mysteriously disappeared.With the emergence of a new murder case and the addition of trainee police officer Lin Jiajia (played by Ding Guansen), she discovered from clues that the murder case was related to Zhong Wei's disappearance.But in the process of handling cases, criminals are always one step ahead. They suspect that there is a mole within the police station... After experiencing a series of criminal incidents and confusing cases, can they defeat the darkness and find the truth behind it?