Episode 3 of "Queen Mantis" opens with a haunting flashback to a younger Choi Jeong-ho, who remarks on the chaos reigning in 2001, a year marred by sudden and widespread unemployment. With despair looming large, crime rates soar, particularly incidents of sexual assault. Amidst one such harrowing crime scene, I-shin makes her entrance, observing as the alleged perpetrator taunts Jeong-ho. In a twist of fate, this very culprit becomes I-shin's second target.
Fast forward to the present, and the tension is palpable as the situation teeters on the brink, but Su-yeol steps in to rescue Tae-seok from the jaws of danger. In a gesture of gratitude, Su-yeol brings I-shin her favorite coffee. Her curiosity piqued, she inquires about a gunshot wound. A flashback unveils Jeong-ho confessing that I-shin had stipulated a second condition for her cooperation – that he safeguard Su-yeol. Back in the present, Su-yeol's question about whether she misses him is met with evasion. As he departs, a bittersweet smile graces his lips, triggered by a cherished memory of them frolicking at the beach.
The investigative unit regroups, piecing together clues that suggest Gu-wan is not the copycat killer they've been hunting; instead, he's solely culpable for the attack on Tae-seok. His makeshift shrine hints at a Mantis-style murder shrouded in secrecy, the very first of its kind.
During a brief respite, Su-yeol pays a visit to Jung-yeon, only to be interrupted by A-ra's playful teasing. As he hastily leaves, a sinister figure is revealed, lurking in the shadows, having staked out their abode and rigged it with listening devices.
That night, Su-yeol shares his theory about I-shin's inaugural murder with Jeong-ho. Simultaneously, the copycat unleashes his fury on a third victim, mirroring I-shin's third murder with chilling precision.
As the police delve deeper into the case, Jeong-ho has an epiphany – I-shin had indeed sent Gu-wan a letter, urging him to persevere. He surmises that this act of empathy spurred Gu-wan to target his half-brother.
Distraught, Su-yeol confronts I-shin, demanding answers about the first murder and questioning her motives behind manipulating both Gu-wan and himself. He accuses her of not seeking him out out of nostalgia. In a fit of anger, he declares his indifference towards her and his lack of desire to ever see her again. As he storms off, I-shin's face contorts with rage. Later, she discreetly retrieves leaves concealed in her mouth and stashes them away in the false ceiling of the bathroom.
There are even more mirrors strewn about the third crime scene, and the police deduce that the copycat killer is taunting them, pushing their patience to the limit. The victim, it turns out, is blameless, with only an injection mark as evidence of foul play. Frustration consumes Su-yeol, and in a moment of weakness, he loses his composure in front of the prying media lenses.
Concerned, Mr. Jeong dials Su-yeol's number, hoping against hope that he hasn't crossed paths with his mother. But fate has a cruel twist; Jung-yeon answers the call, her world shattering as she realizes Su-yeol isn't the orphan she believed him to be. Jeong, sensing the tension, abruptly ends the call, leaving Jung-yeon in a state of shock. She keeps this revelation to herself, not daring to burden Su-yeol with the news. He remains his typically cheerful self around her, shielding her from the grim realities of his case. Yet, deep down, she yearns for him to confide in her, to share his burdens instead of shouldering them alone. He insists it's merely to spare her worry.
As the investigation progresses, a perplexing pattern emerges: all the victims' phones have vanished without a trace. Suddenly, a breakthrough! They manage to ping the location of the third victim's phone to a desolate, abandoned home. Sung-gyu, ever the skeptic, suspects a trap, but the lure is too strong, and they rush to the scene regardless.
Meanwhile, Jung-yeon, driven by curiosity and a nagging sense of unease, attempts to dig up information on Su-yeol's mother, only to hit a dead end. A-ra urges her to let go, insisting that the past should remain buried. But Jung-yeon is resolute, deciding to embark on a journey to Su-yeol's hometown in search of answers.
At the abandoned home, Su-yeol's eyes fall upon a yellow desk, eerily reminiscent of the one his father had crafted for him with love. Memories flood back—happy times spent with his dad, like the day they played ball, only for it to plummet into their well. Hyuk stumbles upon a tub filled with water and a ball bobbing on the surface. Alarm bells ring in Su-yeol's mind, and he frantically searches for the well. And there, nestled in the darkness, lies the phone, a lifeless corpse, and a chilling message congratulating them on their "find."
The corpse is identified as Jeong Won-sik, who had vanished without a trace three months prior. His company was instrumental in digitizing criminal records, affording him access to I-shin’s case files. The killer had acted on impulse, playing a macabre game with Won-sik before ending his life with a pair of fabric shears. The unit members note that the modus operandi doesn't align with any of I-shin’s previous murders. They theorize that the killer had exploited Won-sik to gain access to I-shin’s case files, suspecting a copycat at large.
Su-yeol ponders whether the crime bears any resemblance to I-shin’s inaugural murder. Could her first victim have been his father? Driven by a haunting suspicion, he returns to the derelict house and descends into the well. There, he discovers his childhood ball, a skeletal remains, and a wedding ring. The abandoned house, it turns out, was once his family home.
A fragmented memory resurfaces: I-shin, drenched in blood, cackling maniacally beside the well. He recalls her later casting a ring into its depths. Consumed by fury, Su-yeol storms into the safe house, confronting her. To his astonishment, I-shin not only admits to the accusations but also declares that slaying her drunken, abusive husband was the most exhilarating experience of her life. She claims she did it for Su-yeol's sake.
Confused, Su-yeol listens as she insists he has lost his memory. Horrified, he hears her recount with chilling nonchalance how effortlessly she had taken a life. She had never confessed, she explains, because no one had ever inquired.
Through a haunting flashback, the truth unravels. Her husband, reeking of alcohol, menaces her. Su-yeol, in a desperate bid to shield her, intervenes, only to be brutalized by the man. In a split second of desperate resolve, I-shin plunges the fabric shears into her husband's chest to save Su-yeol. In shock, she hurls his lifeless body into the well. As rain begins to pour, she realizes her liberation from his tyranny and erupts into maniacal laughter. The rain washes away the blood, and she tells everyone he had abandoned her.
In the present, she smiles, acknowledging that this act had ignited her insatiable bloodlust. She laments not having inflicted more pain on her husband. Distraught, Su-yeol concludes that she hadn't killed her victims as retribution but because she relished the act of killing. Overcome by a mix of emotions, he tries to strangle her. To his horror, she revels in the shared desire to kill, urging him to end her life. He screams in anguish, unable to reconcile the monstrous truth before him.
