The fifth episode of "Nine Puzzles" kicks off with an unsettling scene where someone meticulously sketches Chi-mok's dismemberment on the third puzzle, subsequently sending it to I-na. Puzzled and disturbed, I-na grapples to decipher its meaning until the harrowing realization dawns upon her: Chi-mok was the intended victim of the enigmatic puzzle killer. Shockingly, the killer manipulated Yang-hee into unknowingly executing his grim plan.
I-na ventures to visit Yang-hee behind bars, where they delve into the intricate layers of the puzzle. The widow, finally grasping her unwitting role in the deceit, recounts how she and Jae-wook transported the suitcase to the lake. The puzzle killer's cunning plan to forge wheel treadmarks led the authorities straight to the suitcase, revealing Yang-hee's false involvement.
In a chilling turn of events, a new murder rocks the community – Choi Young-han, a veteran factory worker who had recently returned from a year-long sabbatical, perishes after consuming soju laced with nicotine during a festive gathering with three colleagues in the break room.
Drawn by curiosity, I-na arrives at the scene, where she encounters Sergeant Nam. She attempts to forge a connection by mentioning their shared experience at the therapy clinic, but the cop pretends ignorance, much to the amusement of the onlookers. Han-saem, ever the skeptic, is irritated by I-na's presence, bewildered by his inability to dissect her character and put an end to his lingering resentment.
Turning her attention to the case, I-na scrutinizes the crime scene, finding it meticulously clean and clinical. CCTV footage reveals the three coworkers arriving around 8 pm and exiting at staggered times, casting suspicion on all three. Each colleague becomes a potential suspect as accusations fly, with Jung-chul being the one to stay behind and report Choi's demise, Gap-je bulk-ordering nicotine and announcing his departure, and Deok-mun purchasing soju despite being a teetotaler. He also claims to have visited his mistress before the gathering, yet no clear motive emerges, as all maintained amicable relations with Choi.
By sheer coincidence, I-na and Han-saem converge in the break room, where they delve into the intricacies of motive. Han-saem, drawing inspiration from his avid love for detective novels, begins to piece together clues. Enthusiastic I-na persists in dragging him to her place, compelling him to engage in a role-playing exercise, portraying various suspects. Initially hesitant, Han-saem gradually finds his stride, wrapping himself in the characters' personas. Their collaborative efforts ultimately steer them towards the possibility that the killer could be an entirely different individual, focusing their suspicion on Janitor Yeom, a smoker who harbored no fondness for the break room revelry. Yet, his motives remain murky, prompting him to disclose a stunning revelation from a year past.
Frustrated by the apparent lack of a compelling motive, I-na vents her frustrations to Dr. Lee. The therapist, with perceptive insight, suggests shifting the focus to the victim himself, posing the question: Was he ever truly meant to be the target? Han-saem learns from Yeom that Choi's son, Dong-kyung, had passed away a year earlier, a piece of information he fails to share with I-na initially, leaving her upset. Sheepishly, he joins forces with her to pursue this lead.
Their investigation leads them to Choi's residence, a stark and orderly space adorned with a solitary photograph of the four men. The scene reminds I-na eerily of her friend's house, who had attempted suicide, maintaining a similar meticulous tidiness. A revelation dawns upon I-na: Choi might have orchestrated his own death, framing the three men as an act of retribution.
The interrogation of the three suspects intensifies, centering on Dong-kyung's fate. Flashbacks reveal a shared fondness for the boy, interrupted one day when Choi was absent. The suspects entrust Dong-kyung with a perilous task, stepping away for a brief respite. Their world shatters when Dong-kyung's arm becomes trapped in machinery, and despite their urgent return, it is too late to save him. In the aftermath, the trio devises a plan to conceal their tragic mistake before summoning the authorities. Presently, their faces mirror sorrow and guilt.
Another memory resurfaces, depicting Choi spiking the soju. As the festivities commence, Gap-je is summoned away on duty, Deok-mun steps into the restroom, and Jung-chul drifts into slumber. Unbeknownst to them, Choi consumes the poisoned drink, wracked with convulsions before succumbing to his fate. The narrative unfolds, painting a picture of deceit, guilt, and the tragic consequences of a momentous error.
During her therapy session, I-na struggles to comprehend Choi's decision, branding it as a haphazard display of poor planning. Dr. Lee, taken aback by her frustration, offers insight into human behavior in adverse scenarios: while some resort to taking the lives of others, some turn the blade inward. She draws a parallel between Choi and I-na, emphasizing their shared tendency to withdraw and shut down when confronted with overwhelming challenges. I-na, initially chagrined by this portrayal of her fragility, suddenly sparks with an idea.
Determined, she once again breaks into Han-saem's apartment, this time armed with a bottle of soju. With a playful challenge, she tasks him with guessing which category she falls into. Recognizing, as Dr. Lee did, that I-na possesses no inclination towards harming others, Han-saem accepts the soju, unperturbed by any notion of it being poisoned. Indeed, it is safe, and he remains unscathed.
Relieved that Han-saem has placed his trust in her, I-na unveils a novel hypothesis. She suggests that the enigmatic figures within the puzzle might in fact be the perpetrators themselves, implying that the puzzle killer's victims could be the guilty parties. Dong-hoon, Mi-young, and Chi-mok could potentially have inflicted pain upon the elusive puzzle killer. Furthermore, she posits that to fully unravel the puzzle, six more culprits might meet their fate.
As Nine Puzzles Episode 5 concludes, an imposing puzzle is meticulously assembled, revealing the visage of an individual, leaving the narrative teetering on the edge of revelation.
