Episode 9 delves deeply into Je-na's harrowing backstory, illuminating the intricate tapestry of her transformation. Once, she was a doting sister, willing to relinquish victory to Je-yi purely for her sibling's joy. But the tables turned when Je-yi no longer saw her as indispensable. As their father's affection pivoted solely towards Je-yi, Je-na felt the cold sting of abandonment. Desperate to reclaim a semblance of recognition, she resorted to fabricating illnesses, hoping to evoke pity.
The pivotal moment arrived when her father vowed to give her his undivided attention—provided she excelled. Driven by a relentless quest for his approval, Je-na slipped into a spiral of paranoia. She turned to drugs as a means to amplify her academic prowess, a path that led her to a perilous extreme: breaking into her school to pilfer an exam paper. Her scheme unraveled when Seul-gi's father caught her red-handed. Instead of exposing her, he offered silence in exchange for undisclosed favors. Seizing this fragile lifeline, Je-na seduced him, unknowingly ensnaring herself in a web of deceit as a security camera captured every intimate moment, with her father, Yoo Tae-jun, as a silent, horrified observer.
The narrative shifts to the present, where Je-yi confronts Je-na head-on. In a frantic bid to seize Je-yi's phone, Je-na lunges, but the phone slips from their entwined fingers, plummeting out the window. Before Je-na can retrieve it, security personnel arrive, forcing her to flee. Je-yi, however, manages to snatch the phone from its perilous descent.
Elsewhere, chaos reigns as Seul-gi is brutally assailed, prompting the school to implement a lockdown. Ye-ri, hiding in a secluded room, overhears a hushed conversation that ties the attack to drugs. Meanwhile, Choi Gyeong surreptitiously snatches the weapon used in the assault, fully aware that the school might attempt to hush up the incident. Her plans are foiled, however, when her mother intercepts her and confiscates the knife.
Je-yi, apprised of Seul-gi's critical condition, rushes to her father's hospital, where he tends to her wounds. Simultaneously, the school undergoes a rigorous drug sweep. Je-yi's business partner, Cho A-ra, grows increasingly frantic as a video documenting Seul-gi's assault goes viral, stirring fears of identity exposure and plunging them all into a maelstrom of dread.
When Seul-gi finally regains consciousness, Je-yi confronts her head-on, accusing her father of indulging in inappropriate relationships with his students. However, Seul-gi is deeply offended by the allegations and storms off in a huff, leaving Je-yi stunned.
Later, Byeong-jin urgently summons Je-yi to the hospital to fetch some painkillers. While there, Je-yi catches a glimpse of a body bag being surreptitiously brought into her father's clinic, under his watchful eye. Intrigued and disturbed by the scene, she decides to investigate further. To her shock and horror, she discovers a lifeless body lying inside the bag, bringing the episode to a chilling and unsettling close.
