Episode 1 of *Queen Mantis* opens in October 2025, amidst the haunting stillness of a crime scene by a gurgling stream. The victim, a convicted sexual offender released on parole, lies lifeless—strangled, his tongue severed and cruelly forced into his rectum. Chief Choi Jeong-ho is instantly thrust into a whirlwind of flashbacks to October 2001, when he first crossed paths with the notorious Mantis: a female serial killer with a penchant for targeting abusers. One by one, her victims suffered grotesque fates—mutilated, beheaded, and drowned—as months of fruitless investigation finally culminated in her arrest following a chilling confession.
Fast forward to the present, and the Major Crimes Unit at Nambu Precinct finds itself grappling with this copycat’s gruesome handiwork. With no leads in sight, the pressure mounts, culminating in Detective Kim Na-hee collapsing under the strain. Yet, her reputation as a tenacious officer precedes her, with whispers of an impending promotion to squad leader swirling around.
Meanwhile, in the stark contrast of Anwon Prison, Mantis—real name Jeong I-shin—lives a life of unexpected luxury, her days filled with melodies from her headphones and the strokes of her sketchbook. Her world is not devoid of love, for she harbors a deep affection for her son, Jeong-ho. Upon hearing of the copycat’s deeds, she pens a letter to Chief Choi Jeong-ho, her words laden with unspoken meanings.
In a parallel narrative, narcotics detective Su-yeol is embroiled in a harrowing case. A drug-addled woman, in a fit of desperation, stabs her husband to death and turns her blade on her own daughter, Eun-ae. With no clear shot, Su-yeol makes a split-second decision, risking it all to shoot the assailant in the leg. His actions, however, land him in hot water as his superior grumbles about the complications of dealing with a traumatized child until Child Protective Services intervenes. It is then revealed that Su-yeol, once a vulnerable child himself, shares a harrowing past with Eun-ae—he is none other than Jeong-ho, Mantis’ estranged son.
Back at Nambu Precinct, Chief Choi Jeong-ho engages in a tense discussion with Hong, his former boss now elevated to commissioner. Both men are seething with resentment over Jeong I-shin’s cushy existence in prison—a condition of her confession that now seems like a bitter pill to swallow. The urgency to apprehend the copycat intensifies, fueled by the fear that public scrutiny over I-shin’s whereabouts may soon turn into a storm they cannot weather.
Even if it entails meeting her, the situation remains unchanged. I-shin has extended her offer to assist in apprehending the killer, yet she insists on conversing with Su-yeol only in the cozy confines of a homely environment. Desperation grips Jeong-ho as he unveils the deal to Su-yeol, only to ignite the latter's wrath. Su-yeol, known for his quick temper, rejects the proposition with fervent vehemence. He retreats to the sanctuary of his home, where his wife, Jung-yeon, a ceramic artist, awaits.
That very night, the copycat strikes once more, plunging the city into terror. Memories of Jeong-ho's past words resurface in Su-yeol's mind, reminding him of how he could ease the guilt he harbored over his mother by donning the mantle of a policeman. Compelled, he concedes to the deal, though he finds it absurd that I-shin's insistence stems from a longing for his presence. His paranoia is heightened by the setting—an ex-NIS safe house, guarded by a solitary sentinel.
Consciously, he conceals his wedding ring, but I-shin, with a keen eye, spots the telltale mark it leaves. As she attempts to engage in idle chit-chat, Su-yeol's fingers curl involuntarily, a silent gauge of his simmering anger. He maintains a formal demeanor, drawing a clear line in the sand. I-shin, too, exhibits a similar nervous habit—her fingers curling as she expresses discontent with his icy conduct. Nevertheless, she acquiesces to play along, offering her enthusiastic insights on the case.
Su-yeol's resolve crumbles, and he confronts her, questioning whether the copycat's atrocities and the ensuing carnage bring her amusement. Jeong-ho, sensing the impending escalation, intervenes to terminate the meeting. Yet, I-shin's resolve remains unshaken; she yearns to contribute, even requesting permission to visit the crime scenes.
Su-yeol remains skeptical, but Jeong-ho divulges a startling revelation: he had no tangible evidence when he arrested her. Under immense pressure to secure a conviction, a confession was his sole recourse. I-shin, aware of this predicament, still chose to strike a deal. Jeong-ho asserts that she adheres to a peculiar code of honor, fulfilling her agreements with unwavering loyalty, for she abhors the weight of indebtedness.
Meanwhile, Eun-ae has been placed under the care of Pastor Jeong from Jusin Church. Pastor Jeong makes his way into town to pay Su-yeol a visit. As it turns out, he was also the one who took care of Su-yeol when I-shin was apprehended. Su-yeol pours his heart out to Pastor Jeong, admitting his struggles with anger issues and how he keeps seeing I-shin's face in Eun-ae's mother. He's still haunted by nightmares where I-shin is always grinning at him, even as she commits heinous acts. Concerned, Pastor Jeong attempts to dissuade Su-yeol from seeing Eun-ae again. Their conversation is abruptly interrupted when Su-yeol hears something eerie, though there's no one in sight. Downstairs, Jung-yeon is receiving a visit from her friend, A-ra.
Shifting gears to the case at hand, Na-hee expresses her desire to meet I-shin, but Jeong-ho firmly refuses, insisting on keeping the consultation confidential. To compound the tension, Su-yeol arrives as the new squad leader. The rest of the unit is visibly perturbed, but Na-hee maintains her composure. They brief him on the case, and Su-yeol's attention is drawn to a mirror present at the second murder scene. He recalls that there was no mirror at I-shin's second crime scene. Moreover, the second victim is not an abuser, suggesting that the copycat might be adding his own twisted touches to the murders.
That night, a bespectacled man leers at a sleeping family before retrieving several syringes.
The unit gathers for a team dinner, and Su-yeol extends his apologies for joining the investigation midstream. He vows to prove his worth, and the unit decides to give him a shot.
The following day, I-shin is escorted to the second crime scene. A record player, blaring opera music, stands as a stark reminder of her own crime scene. She poses a perplexing question: how does the copycat know every minute detail about her crime scenes when only one photo has ever been made public?
The scene then shifts to the bespectacled man waking up. The family lies bound and gagged, their heads covered.
Returning to I-shin, she remains tight-lipped about her theory. Frustrated, Su-yeol delves into the news article about her second murder. He notices that the crime scene photo is flipped. Yet, the copycat has replicated I-shin's actions with chilling precision in the same direction. The unit comes to a startling realization: the copycat has access to the Mantis case files. I-shin can't help but look pleased as Su-yeol pieces the puzzle together.
