Episode 4 of "Hunter with a Scalpel" kicks off with Se-hyun being unfairly accused of feline homicide by a local businessman, who had previously reprimanded her for feeding stray cats. Now, pointing a finger of suspicion, he claims to a policeman that Se-hyun must be behind the cat's demise. Understandably, the accusation crumbles under scrutiny, and Se-hyun exits the confrontation in a foul mood.
Arriving at her workplace, Se-hyun's spirits remain dampened until she receives a call from Jung-hyun. He informs her that, thanks to her tip about the large vehicles, they have apprehended a suspect. Eagerly, Se-hyun dashes to the police station and presents Jung-hyun with the soil analysis report, affirming that the murder scene was not where the body was discovered.
Jung-hyun then unveils CCTV snapshots of a white truck spotted in the vicinity of the restaurant where Lee Yeon-ju was later seen. Se-hyun, driven by curiosity, requests to confront the suspect. Jung-hyun, albeit reluctantly, grants her wish, and they step into the interrogation room. Upon laying eyes on the suspect, Se-hyun's tension melts away, replaced by a sense of relief.
Later, Jung-hyun and Chang-jin grill the suspect, Kwon Hyung-jo, who steadfastly denies being the man in the photo near the restaurant. He confesses to his peculiar profession: delivering sex dolls, which can eerily resemble real humans. This confession is corroborated by the discovery of such dolls at his warehouse, verified by another officer.
When Chang-jin interrogates him about stalking, tensions escalate into a brawl, leaving Hyung-jo injured. He demands an apology from the officers, but Jung-hyun steps up, taking personal responsibility and refusing to let Chang-jin kneel in contrition. Jung-hyun reminds Hyung-jo that, though he may escape the label of murderer, he is undeniably a stalker.
Hyung-jo storms out of the police station, his voice resonating through the air as he accuses the officers of assaulting him, drawing a cluster of reporters nearby. Inside, Choi Jong-soo, Jung-hyun's supervisor, reprimands Jung-hyun and his team severely. In response, Jung-hyun concedes to rectify the situation by addressing the reporters in a public briefing about the ongoing case.
As Jung-hyun drafts his speech, Chang-jin and his colleagues uncover CCTV footage captured by Se-hyun and Min-ho during their commute home. The tape reveals a figure clad in attire identical to Hyung-jo's, who casts suspicious glances at the two doctors before trailing them out.
Jung-hyun then proceeds to front the public briefing regarding the murder cases. However, as reporters pepper him with inquiries, he finds himself momentarily paralyzed. At this critical juncture, Se-hyun steps in beside him, seamlessly seizing the reins. She announces to the gathered media that identical fingerprints have been discovered in both murder scenes, marking this as a serial killing spree.
With a fiery tone, she labels the perpetrator as nothing short of human scum. Meanwhile, Choi Jong-soo watches the unfolding scene on television, his face a mask of disappointment, while a young girl named Se-eun looks on from the comfort of his home.
After her compelling brief, Se-hyun exits the hall only to receive an irate phone call from her boss. But upon her agreement to conclude the Nam Seung-hyeop case according to his wishes, his anger subsides. She subsequently instructs him to establish a forensic office in Yongcheon, where she intends to collaborate with Jung-hyun on the case.
Shortly thereafter, a senior officer summons Se-hyun and Jung-hyun, accusing them of stirring chaos by branding the crimes as serial killings. Se-hyun retaliates by warning him that the killer's reign of terror will persist unless stopped. She vows to work tirelessly alongside Jung-hyun to apprehend the culprit.
Jung-hyun convenes a meeting with his colleagues, positing that the perpetrator likely possesses intimate knowledge of Yongcheon and harbors a superiority complex. He galvanizes them to unify their efforts in solving the case.
Elsewhere, at the laundromat, an enraged customer bursts into Choi Jong-soo's shop, demanding a refund for a ruined garment. Initially compliant, Choi's demeanor quickly shifts to one of menace. As the customer attempts to flee, Choi yanks her back, the scene escalating tension.
