Episode 3 of "A Killer Paradox" unfolds not with Tang at the forefront but with Yeo-ok stealing the spotlight. A haunting flashback transports us to a younger Yeo-ok, leisurely spending time with her friends as she casually lights up a cigarette. However, fate intervenes in the form of a gas leak, culminating in a catastrophic explosion that shatters her life—leaving her with a missing eye and scars etched across her skin. Transitioning to the present, an adult Yeo-ok is seen manipulating a pipe, funneling gas into her parents' bedroom with sinister intentions. Her mother's unexpected awakening foils her plot, prompting Yeo-ok to seize a knife with a glint of determination in her one remaining eye. It transpires that she had cunningly enrolled her parents in eight life insurance policies.
Meanwhile, a chilling narrative about Yeo-ok's past circulates online, asserting that even death could not expunge her sinister deeds. Nan-gam stumbles upon this posting and reads it in its entirety, his curiosity piqued. Alongside Yong-jae, he tracks down the author—a cousin of Yeo-ok's. This cousin recounts a harrowing tale of Yeo-ok pouring boiling water on her face during school days, motivated by nothing more than a twisted pleasure in causing pain.
At the police station, Chung-jin is greeted with congratulations upon his return to duty. He briefly recounts the stabbing incident before steering the conversation towards the unsolved murders of the two boys. Later, in a private discussion with the captain, Chung-jin reveals his desire to abandon his law enforcement career and pursue a new path as a sashimi chef.
Nan-gam and Yong-jae attend the funeral of one of the high school victims. Nan-gam boldly inquiries about the victim's mother regarding his aggressive encounters with Chung-jin, earning a swift slap in response. Yong-jae finds himself questioning the appropriateness of Nan-gam's tactics. During their return journey, Nan-gam shares a haunting story from a previous case he worked on, adding a layer of depth to their already complex investigation.
A young girl named Kang Yeon-seo took her own life following a brutal rape orchestrated by two boys. During her solemn funeral rites, the mother of one of the perpetrators boldly entered the premises, creating a disturbance and insisting that the act was consensual. Nan-gam, who had recently encountered the woman, revealed that she was indeed the mother of the accused rapist. He emphasized that individuals are not merely perpetrators or victims; they can occupy both roles. Tragically, the boy continued his spree of assaults and thefts, which had prompted Nan-gam to set his sights on him and his accomplice in Episode 1.
Nan-gam sought information from the convenience store owner, who mentioned that Yeo-ok had been standing nearby at around ten o'clock. When the detective inquired about Lee Tang, the owner flew into a rage, recounting how Tang had deceived him out of his money. He also mentioned that Tang had spotted the woman in question.
Back at his residence, Tang received a message from the Only For Heroes Telegram user. Upon realizing that the user knew his name, Tang was struck with fear and promptly blocked him. Soon after, a postman arrived with a court summons for Tang, notifying him of a hearing regarding his theft of money from his employer.
Nan-gam engaged in a heartfelt conversation with Chung-jin, urging him not to abandon his responsibilities. Chung-jin, however, was resolute and returned home, where his wife informed him that Nan-gam had gifted their son a bicycle. Meanwhile, Nan-gam met with the detective handling Tang's financial fraud case.
Elsewhere, Yong-jae visited the home of the girl featured in Nan-gam's narrative. Unexpectedly, Yeon-seo's father, Sang-muk, confessed to the shocking act of murdering the boys who raped his daughter. In a parallel development, Tang made the courageous decision to surrender. He contacted the detective overseeing his financial fraud case and conveyed his intentions. Misunderstanding Tang's motive, the detective instructed him to come by at 9 pm. Tang set aside some money for his mother and the convenience store, packed all the evidence of his crimes into a bag, and left his house, stepping into an uncertain future.
Sang-muk delivers his confession, asserting that he dispatched the boys with a brick but drawing a blank on its subsequent whereabouts. Nan-gam, skeptical of his tale, storms into the interrogation chamber and unmasks the perpetrator's deceit – the man who claims no affinity for tobacco yet his victims bore cigarette burns, and who is naturally left-handed, contrary to the murderer's right-handed prowess. Nan-gam's supervisor, irritated by the revelation, is however persuaded by his subordinate's arguments. A subsequent message from another detective alerts Nan-gam to Lee Tang's involvement. Yong-jae, regretting his hastiness, reveals he has informed the high school boy's mother of their suspect, querying if this might pose an issue.
A memory flashback unveils Sang-muk receiving a knife in a mysterious package at his abode, firmly setting his resolve to eliminate the boys. He exchanges messages with the same individual who had contacted Tang, the enigmatic OnlyForHeroes, urging him to execute their rehearsed plan.
Presently, a dramatic twist unfolds as a car, driven by the high schooler's mother, collides with the man just outside the police station. Meanwhile, Tang deposits his earnings into an ATM, but his luck takes a dive when two bike-riding thieves snatch his bag and flee. Finding little cash within, they discard the bag along with incriminating evidence of Tang's grim deeds. Tang, sustaining an arm injury in his fall, is whisked away in an ambulance to a hospital.
Sang-muk, himself confined to a hospital bed, faces Nan-gam's probing questions about why he would frame himself while shielding the genuine perpetrator. After Nan-gam's departure, Sang-muk receives another text from OnlyForHeroes. Spotting Tang exiting with a bandaged arm, Sang-muk attempts to follow but his wheelchair topples over. Tang, hearing the commotion, returns to investigate. Sang-muk, wary of the police's presence, urges Tang to depart but hints at further communication via Telegram. Tang, realizing his identity is compromised, tries to extract more information, but Sang-muk deflects, promising to reconnect on the messaging platform. Tang hastily retreats, but unfortunately, Nan-gam catches sight of him and begins to trail him.
Sang-muk finds himself engrossed in videos featuring his daughter, each frame evoking cherished memories they've shared. Overwhelmed by nostalgia, he reaches for a cluster of his sleeping pills and consumes them without hesitation. A sudden flashback transports him to a scene where Tang, with fierce determination, confronts two boys and, with a brick in hand, delivers devastating blows to their heads, ultimately collapsing as if engulfed by darkness.
Just as Nan-gam trails Tang, an urgent call pulls him back to the hospital—Sang-muk's condition has worsened. Tang opens his Telegram account to a blank screen, realizing it has been deleted. His mind races back to being carried home by two figures, not a solitary one.
Inevitably, Tang's sister and mother arrive at his apartment, seeking him out with concern etched on their faces. But upon entering, they find the space eerily barren, as if it had been prepared for an absence. A haunting flashback unfolds: Sang-muk, clinking glasses with a companion, opens up about Yeon-seo's agonizing end. She lingered in the hospital, suffering for hours before finally passing away. Sang-muk confesses his desire for revenge against those who inflicted such pain. The younger man opposite him, clad in a Batman hoodie, offers a solution, hinting at a course of action that could grant him justice.
