Luo Weizhao’s team identifies a suspect, Zhang Donglan, who is connected to a high-profile group and the SID chief. Pei Su, with his own ties to the case, undergoes questioning.

An anonymous tipster, Chen Zhen, implicates a drug ring in his sister’s death. Tension escalates when the victim’s mother confronts Zhang Donglan after his release.

The investigation uncovers new truths about a cold case, and two new interns, including Pei Su, join the SID