Episode 3 of GG Precinct delves deeper into the mysterious death of Yumi, a
popular singer. The episode opens with a flashback to 2001, where Chang and the
future Commissioner are interrogating Shui-yan, a notorious serial killer.
Shui-yan taunts them, offering to reveal the idioms he used to kill two
students. However, he demands to speak to the Commissioner alone, who is forced
to comply. In a shocking turn of events, Shui-yan attacks the Commissioner,
leading to a chaotic struggle before being subdued by guards.
In the present day, the precinct investigates Yumi's death, believing that her stalker fan, Hsieh Cheng-ta, may be involved. However, they find his house empty and covered in defamatory messages about Yumi. Meanwhile, Tzu-ching notices Ming-han missing and discovers him at Yumi's place. A dangerous chase ensues when a hooded figure attacks Ming-han, attempting to run him over with a car. The assailant is revealed to be Pai-sheng, Yumi's manager.
Chang visits Shui-yan, who is now incarcerated at the precinct. He recalls Shui-yan's previous taunts and asks how he knew the third idiom. Shui-yan agrees to reveal the secret, but only to Tzu-ching. As Tzu-ching and Ming-han argue about the potential culprits, Cheng-ta arrives at the precinct. He claims to have witnessed Pai-sheng harassing Yumi.
The precinct's investigation takes a new turn when the coroner, a Yumi fan, recognizes Cheng-ta from her concerts and attempts to attack him. Chang calms him down and brings him on board as a Yumi expert. Cheng-ta reveals that he had delivered gifts to Yumi's place and overheard her arguing with Pai-sheng. He believes that Yumi was afraid of Pai-sheng and ran into her apartment to escape.
Pai-sheng presents a different version of events, claiming that he was at Yumi's place to sell her fan gifts. He denies any involvement in her death and insists that Cheng-ta was the one who harassed Yumi. However, the precinct finds inconsistencies in his story, including his poor vocabulary and his connection to Huang Hsien, a teacher mentioned in Shui-yan's idiom book.
Tzu-ching questions Shui-yan, who manipulates her by playing on her insecurities. He reveals that he knew the third idiom because it was part of a specific sequence in his idiom book. Both Tzu-ching and Shui-yan conclude that the killer must be one of Shui-yan's former students. The precinct begins to investigate the suspects' school records and shows Shui-yan their photos.
As the episode concludes, Ming-han arrives with Huang Hsien's idiom book, asking Shui-yan if he knows him. Cheng-ta is seen leaving the precinct, heading towards Hsien's Chinese course. The final scene shows a group of students and a man praying to Shui-yan's idiom book in Hsien's classroom, hinting at a potential connection between the killer and Shui-yan's teachings.