Episode 5 of *Queen Mantis* opens in the year 2002. Jeong-ho apprehends I-shin on suspicion of murder. He has been meticulously tracking her movements, and the discovery of her hairpin at one of the crime scenes serves as damning evidence. Yet, as she is taken into custody, a mocking laugh escapes her lips, for she knows that this circumstantial evidence is far from conclusive. Little does Jeong-ho realize, however, that I-shin has been keeping tabs on him as well. Leveraging his inherent compassion, she strikes a deal: in exchange for her confession, he must ensure that her son is cared for.
Fast forward to the present, and a tense reunion unfolds between Jung-yeon and I-shin. I-shin calmly explains that she faked her own death to prevent any discord from arising in the young couple's marriage. Alarmed, Jung-yeon calls Su-yeol, who races to the scene in a panic. Yet, upon arrival, he finds I-shin as composed as ever, and she departs with him without resistance.
However, when confronted about Gu-wan's demise, I-shin remains tight-lipped, refusing to confess. Instead, she poses a haunting question to Su-yeol, inquiring whether he feels a sense of relief at Gu-wan's passing. The question rattles Su-yeol, evoking memories of Gu-wan's chilling accusation that Su-yeol is just as bloodthirsty as I-shin herself.
Meanwhile, a desperate Jeong-ho is on the verge of confessing to his team and enlisting their help in locating I-shin. His resolve wavers, though, when he receives a text from Su-yeol, assuring him that I-shin is under control. The unit is left even more bewildered when they learn that Min-jae has been released, his alibis having been verified.
Commissioner Hong, under immense pressure to deliver results, issues a stark warning to Jeong-ho: either he produces something substantial, or additional officers will be brought in, jeopardizing Su-yeol's covert identity.
As the unit intensifies its efforts to uncover the truth behind Gu-wan's murder, Na-hee's curiosity about Su-yeol grows. She recalls his relentless drive to save lives, a trait that both intrigues and puzzles her. Meanwhile, Sung-gyu enlists Ji-an's help to delve deeper into Min-jae's background, determined to uncover any hidden secrets.
Su-yeol drops Min-jae off at his home, issuing a stern warning not to idolize a serial killer. He asserts that I-shin rationalizes her choice of victims, but in reality, she kills because she revels in it. Min-jae is visibly distraught and fires back, accusing Su-yeol of being just like her—rationalizing that his mother is evil so he doesn’t have to grapple with missing her. He insists that, despite everything, his mother loved them. However, the constant comparison to I-shin starts to get under Su-yeol's skin.
That night, Jung-yeon reveals a troubling detail: Su-yeol often calls out for his mother in his sleep. He dismisses it as a nightmare, but Jung-yeon suspects he's not being truthful.
Turning their attention back to the case, Su-yeol and Jeong-ho delve into I-shin’s psychiatrist's records, suspecting that someone might have stolen her file to gain insights into the very first murder. Employing a bit of subterfuge, they manage to swipe the file themselves. Within its pages, I-shin speaks of her husband and recounts witnessing her mother perish in a fire. Su-yeol decides it’s high time they inform the unit about her. However, Jeong-ho urges caution, warning that the betrayal could jeopardize their investigation.
Meanwhile, Min-jae pays a visit to A-ra. Jung-yeon inquires about I-shin’s parenting, and Min-jae genuinely believes she was a good mother.
Elsewhere, Su-yeol questions his grandfather about the fire. Jeong reveals that he stopped I-shin from attempting to save her mother, deeming it too late. From that day forward, she distanced herself from him. He blames himself for her subsequent descent and Su-yeol offers him comfort.
Ji-an, who has been stalking Min-jae, stumbles upon a dating app. He discovers that Min-jae is being catfished by someone named Jo-i, who claims to be a fan of his webtoon. Among Jo-i’s followers are the other copycat victims. Sung-gyu wants to pursue this lead alone, but Na-hee intervenes, insisting that Su-yeol should be informed.
Just then, Su-yeol receives a mobile phone packed with video recordings of all the copycat murders. The killer calls, demanding that the phone be handed over to “the woman.” Fed up with the secrecy, Na-hee and Sung-gyu demand answers. Jeong-ho attempts to shoulder the blame himself and on Commissioner Hong. However, Su-yeol comes clean, revealing that they are collaborating with I-shin.
He apologizes for the deception, and Na-hee fills him in on Jo-i. Jeong-ho also warns Min-jae about the catfish, but Min-jae just finds it amusing.
The unit heads to the safe house where I-shin is cooperating. Yet, she keeps dropping inside jokes that Su-yeol chooses to ignore. The copycat calls again but offers little information. He declares his intention to make I-shin even more infamous and hints that his next victim will meet their end in a manner reminiscent of the final scene.
The police uncover opera singer Kim Seo-jun among the ranks of Jo-i's followers. I-shin remarks that the discovery seems almost too straightforward, yet the team proceeds to the opera theater regardless. Meanwhile, Min-jae, having just completed his webtoon, decides to while away the time by lending Su-yeol a hand. He cleverly lures Jo-i into a meeting by dangling the promise that she could be the first to read the conclusion of his webtoon.
At the opera house, as the final curtain falls, Seo-jun vanishes without a trace. His disappearance stems from a misguided belief that the police are hot on his heels due to his drug-related transgressions. The officers are left disheartened until Su-yeol's eyes catch sight of a message from Min-jae. Just then, chaos erupts at the store as an unknown assailant appears and unleashes a fury of blows upon Min-jae.
Jeong-ho stands by I-shin's side, his voice laced with desperation as he pleads with her to reveal any hidden truths she may be harboring, for her own well-being. He questions whether she truly attempted to take Min-jae's father's life. I-shin defends herself, asserting that she did everything within her power for Min-jae's sake, yet he always seemed to crave more. Suddenly, the copycat calls, thrusting a harrowing image before her eyes—a battered and bound Min-jae hanging precariously.
As Episode 5 of "Queen Mantis" draws to a close, Su-yeol and Na-hee rush to the store, only to find Min-jae lying lifeless. Su-yeol's pleas for him to hold on echo through the air, while Na-hee's face is etched with a look of profound concern.
