Episode 4 of Nine Puzzles kicks off with an intense scene of Kang Chi-mok pounding furiously on a hotel room door. The scene abruptly shifts to a chilling vision of a man being brutally murdered and dissected, accompanied by blaring music that serves as a macabre soundtrack. The severed limbs are packed away in a crimson suitcase, which is then carried off by a figure clad in identical attire to Chi-mok's. With a sinister finality, he hurls the suitcase into the depths of a serene lake.
The following day, the police launch a desperate search for Chi-mok. They stumble upon his car abandoned at a lonely rest stop. Surveillance footage unearths a mysterious individual, donned in Chi-mok's clothes and gloves, exiting the vehicle at 3:17 am. He vanished into the darkness, making a beeline for a formidable boundary wall. Han-saem, struggling to scale the wall, sustains grazing wounds on his hands, adding to the mounting suspense.
I-na crafts a psychological profile of Chi-mok, depicting him as impulsive and hot-tempered—a stark contrast to the calculated demeanor of the unknown killer. Chi-mok's seemingly flawless disappearance raises more questions than answers. The discovery of ropes in the trunk of his car fuels Han-saem's suspicion that he might have staged his own death after strangling Mi-young.
Chi-mok's wife, Seo Yang-hee, insists that he never returned home. However, CCTV evidence contradicts her claim, revealing Chi-mok's arrival and subsequent journey towards the Yeongpyeong Reservoir at 11 pm, culminating at the rest stop at 2:29 am. Further investigation into his credit card activity uncovers a booking for a one-night stay at Y Hotel, a clandestine love nest nestled near the reservoir. Hotel records confirm his check-in at 9 pm.
Inside the hotel room, Han-saem stumbles upon blood splatter on the bathroom sink, a grim testament to a violent altercation. Forensic analysis verifies the occurrence of a bloody assault. The hotel's stringent privacy policy ensures that CCTV footage is routinely erased, but guests' complaints about loud music from the previous night provide a crucial lead. At 2 am, a man dressed in Chi-mok's clothing was spotted departing with a red suitcase.
Driven by an unyielding resolve, Han-saem ventures to the reservoir and uncovers wheel tracks, hinting at the suitcase's journey into the water. Each revelation pieces together a perplexing puzzle, drawing the detectives closer to unraveling the mystery surrounding Chi-mok's fate and the identity of the ruthless killer.
The suitcase, swiftly retrieved, harbors a grim discovery: a disarticulated corpse, lacking hands and head. I-na, meticulously examining the scene, finds no traces of a struggle, leading her to deduce that the victim was incapacitated by a taser from behind upon entering the premises. She informs Han-saem that this crime bears no resemblance to Mi-young’s murder; the suitcase killer operates with precision, whereas Chi-mok is impulsive and ruled by emotion, leaving little room for riddles. Mi-young’s expression of terror captured on CCTV contrasts with the behavior expected if Chi-mok had threatened her—she would have attempted negotiation. I-na postulates that Chi-mok himself could be the suitcase's victim, questioning the logic behind him wearing gloves while driving his personal vehicle. Han-saem's refusal to entertain this theory frustrates I-na. However, DNA analysis confirms her suspicion: Chi-mok is indeed the deceased.
That evening, I-na seeks insight into Dong-hoon from the housekeeper, who reveals a heart-wrenching transformation following his realization that I-na was orphaned. Overcome with grief, Dong-hoon resigned from the police force. Later, confiding in Dr. Lee, I-na laments sleepless nights, questioning her own inaction if she had encountered Dong-hoon’s killer. The mention of an impending dinner date between them the following day introduces a fleeting moment of levity, only marred by Dr. Hwang's unavailability due to a session with Sergeant Nam.
Returning to the case, Chi-mok received a call at 9:40 pm, near his residence. The brutal nature of the murder suggests a personal vendetta. Reviewing interrogation tapes, I-na notices Yang-hee’s swift denial of any knowledge of Mi-young, her reaction all the more suspicious.
I-na visits Yang-hee, embodying her playful yet candid demeanor. Over a harmonious blend of music and coffee, their bond deepens. I-na reveals her awareness of Yang-hee's acquaintance with Mi-young, earning the widow's admiration. Yang-hee, captivated by profiling, unburdens her heart to I-na about Chi-mok's recent lament over gifting Mi-young a luxurious apartment.
Yang-hee vents her frustration about her lack of personal space, confiding that she has never had a room of her own. As an orphan, she shared a home with her grandmother and sister, and after their tragic demise in a house fire, she was once again compelled to coexist. I-na is astonished by their shared, sorrowful histories.
After departing, I-na presents her theory to her analyst team with fervor. She contends that the man at the rest stop, an accomplice, manipulated CCTV footage to mislead the authorities. The perpetrator, she believes, is a meticulous individual whose motive stems from a desire to eliminate Chi-mok from their life. They thrive on solitude and might even resort to murder to preserve it. I-na's superior hypotheses that the killer is a woman—none other than Yang-hee.
Han-saem further uncovers Yang-hee's deception, presenting evidence from Chi-mok's Uber driver, who captured a video of him returning home at 9 PM. Eager to share her insights with Han-saem, I-na, undeterred by his absence, takes matters into her own hands and breaks into his apartment. As always, Han-saem is irritated but listens as she highlights Yang-hee's disinterested reaction to her husband's demise, her primary grievance being the inadequacy of space. Han-saem counters by reminding I-na of her own stoic demeanor when her uncle passed, suggesting a similarity in their emotional responses.
However, he brings Yang-hee in for questioning. Unexpectedly, she accuses Roh Jae-wook, her lover, of involvement. During Han-saem's interrogation of Jae-wook, he portrays Yang-hee as a dissatisfied wife. Yet, Jae-wook's scratched hands betray him as the accomplice, revealing his guilt in the intricate web of deceit.
I-na proposes a daring strategy, pitting them against one another in a game of wits. She teams up with Yang-hee, while Han-saem partners with Jae-wook. The women share laughter and forge a bond, mocking Han-saem's suspicion of I-na as the killer. However, I-na abruptly unveils a shocking revelation – she possesses an identical red suitcase and inquiries about the origin of Yang-hee's. Yang-hee's smile instantly fades.
In a separate room, Han-saem uncovers a dark secret: Yang-hee's friend was falsely accused when her grandmother and sister met an untimely demise. Soon after, the boy vanished without a trace, terrifying Jae-wook, who had received a request to meet with Yang-hee. Han-saem advises that Jae-wook's safety lies in custody and speculates that Yang-hee could be the one who dismembered Chi-mok. Jae-wook, overwhelmed with disgust, confesses everything and guides them to Chi-mok's decapitated head.
The news whispers that Chi-mok might be Mi-young's murderer, diverting the media's relentless pursuit of the police. I-na offers caps as gifts to everyone, yet her gesture seems calculated, aiming to recapture the image of Dong-hoon's killer, who wore a cap. She further asserts that Chi-mok did not slay Mi-young, intriguing Han-saem.
As dinner unfolds with Dr. Lee, I-na expresses her concerns about Yang-hee, fearing she might manipulate others like the widow did. Dr. Lee reassures her, insisting that Yang-hee is authentic and transparent. The Nine Puzzles Episode 4 concludes with I-na receiving a chilling third puzzle – a dismembered man adorned with an armband, encircled by innocent children.
