Episode 4 of GG Precinct delves deeper into the mysterious murder case,
introducing new suspects and unraveling hidden connections. The episode begins
with a flashback to 2001, where Shui-yan, a popular cram teacher, is struggling
to maintain his students due to his strict and unapproachable demeanor. The
director urges him to be more lenient and tell jokes, but Shui-yan insists on
his teaching methods.
In the present day, Shui-yan claims that Huang Hsien was never his student, but he offers to help the precinct by reminding them that the killer likely gained entry to the victims' homes by pretending to be a delivery boy. However, Ming-han and Tzu-ching disagree on the potential culprit, with Ming-han believing Hsien is involved and Tzu-ching insisting that Cheng-ta is the killer.
As the investigation continues, Ming-han goes undercover as a student to infiltrate Hsien's class. Meanwhile, Tzu-ching is tasked with following Cheng-ta. Despite their differences, Tzu-ching eventually agrees to help, motivated by her personal struggles and desire for recognition.
Ming-han discovers that Hsien is a charismatic and popular teacher, but he also notices a strange connection between Hsien and a student named Mu-ting. The precinct's investigation leads them to Chang Po-lun, a small drug dealer who was seen leaving the scene of the first murder. However, their investigation hits a dead end as Chang is not connected to the case.
Ming-han follows Mu-ting on a date with Hsien, only to witness a surprising twist. The delivery girl who frequently delivers to the precinct arrives and confronts Hsien, accusing him of lying to her. Hsien reveals that the delivery girl is actually his sister.
As Ming-han continues to follow Hsien, he witnesses a tense confrontation between Hsien and Mu-ting. Hsien tries to break up with Mu-ting, but she becomes upset and starts speaking in Gen-Z slang, which irritates him. When Ming-han tries to intervene, Hsien flees the scene in his car, leading to a high-speed chase. Hsien is eventually caught and arrested, but he remains unfazed and even quotes an idiom.
The episode concludes with a shocking revelation. Shu-fen discovers that Cheng-ta was also a student of Shui-yan's in 2001. Tzu-ching asks Shu-fen to check the fourth idiom in Shui-yan's book, hinting at a possible connection between the killer and Shui-yan's teachings. As Mu-ting heads home, a figure in a delivery personnel uniform is seen standing outside her house with a hammer, setting the stage for a dramatic cliffhanger.