Episode 3 of Nine Puzzles kicks off with I-na being haunted by the memories of her uncle's grim demise. The news headlines buzz with wild rumors surrounding the internal investigation, stirring up a whirlwind of speculation. Chief Hyun, eager to put an end to the chaos, readily agrees when I-na steps forward, volunteering to delve into the case.
Arriving at Han-saem's precinct, I-na finds him less than pleased to see her. She unburdens her heart about her recollections, but Han-saem suspects she's merely toying with him. A verbal sparring match erupts as he tries to assert his superior position, ultimately escalating to a confrontation with Hyun that earns him no favors.
During her therapy session, I-na admits to analyzing Han-saem, scrutinizing his trustworthiness. She ponders over the mysterious resurgence of her memories, wondering why they chose this moment to surface. Dr. Lee suggests that I-na's inability to confront her past and the shocking murder of Mi-young have compelled these memories to the forefront. However, I-na confesses a lingering skepticism about the authenticity of her recollections.
As the cops gather for a briefing, they uncover that the regular who usually parked in Mi-young's spot had endured a series of harassments—his car was vandalized with scratches and punctured tires until he finally relocated. This oversight inadvertently allowed the killer to utilize the same blind spot to park Mi-young's car.
When I-na enters the scene, she finds the precinct deserted and begins to rummage through Han-saem's desk, noticing intricate paper roses that he crafts meticulously. Choi San suddenly appears, laying claim to the desk, prompting I-na to inquisitively probe about Han-saem's MBTI type and his underlying personality traits. She's relieved to learn that Han-saem conducted a thorough investigation during the Dong-hoon case, which adds a positive note to her growing understanding of him.
Han-saem meticulously scours through the CCTV footage once more, his eyes locking onto the chilling sight of the killer clamping the rope around Mi-young's neck just as she pulls into her driveway. He painstakingly retraces her journey, realizing with a start that the murderer must have boarded her vehicle unnoticed in Griffin's parking lot, a CCTV blind spot. Han-saem ponders deeply, puzzled by why the assailant waited until Mi-young reached the sanctuary of her home to carry out the deed.
Just then, I-na bursts onto the scene, having independently reached the same conclusion. She arrives with a meal in hand, gracefully inviting herself over to his mother's house. Mrs. Kim, beaming with joy, ushers them in for dinner. Han-saem is acutely aware that I-na is subtly analyzing him, yet she cleverly veils her intentions by feigning romantic interest, prompting Mrs. Kim to unwittingly divulge a plethora of personal anecdotes. Through these stories, I-na gleans that Han-saem is genuinely compassionate, often brightening the days of his ailing high school friend.
As they bid farewell to Mrs. Kim, I-na attempts to mend fences with Han-saem, recognizing that in a world where the killer lurks, she desperately needs an ally she can trust. She proposes a mutual profiling arrangement—if he profiles her, perhaps trust can blossom on both sides.
Elsewhere, a breakthrough occurs when a partial fingerprint is discovered on the driver's headrest, a detail overlooked until now. Yang, acknowledging their earlier oversight, expedites the fingerprint to forensics for analysis. Meanwhile, I-na compiles her criminal profile, officially presenting her theory on the serial killer, intricately piecing together the puzzle that has left everyone baffled.
Her contention revolves around the notion that both crime scenes exhibited characteristics of intimate, secluded spaces. The victims had been premeditatedly chosen. Absence of CCTV footage compounded the mystery. Their demises were swift, causing minimal suffering. The perpetrator's motive wasn't recreational; rather, it hinted at a personal vendetta against the victims. Yet, the peculiarity lies in how meticulously executed the murders were, akin to a professional assassination. The investigative team remains unconvinced and rejects her hypothesis outright. Nonetheless, Han-saem stands firm, asserting that her observations carry a ring of truth.
Elsewhere, Sergeant Nam finds herself drawn to Dr. Lee's clinic for a therapeutic session, haunted by the image of Mi-young and grappling with guilt. Her presence startles the second physician who enters the room. Switching back to the case, the detectives heed Han-saem's insights and delve into Mi-young's past. Her family had disowned her; she fled after her mother's demise. Her father, battling dementia, becomes the next focus of their inquiry, prompting Han-saem to visit him. I-na tags along, monopolizing the conversation throughout the journey, much to his chagrin.
At the nursing home, I-na adopts a pretend persona of Mi-young, and Mr. Lee, momentarily lucid, engages with her. When she inquiries about Dong-hoon, he draws a blank. However, he vividly recalls Mi-young's slacker boyfriend, whom he despised intensely. He also mentions a noticeable transformation in her demeanor.
Concurrently, Han-saem interviews the guardian, Cousin Du-cheol, who echoes the sentiment about Mi-young's troublesome boyfriend and her transformation upon returning after seven years. As I-na and Han-saem sift through Mr. Lee's abode, they uncover Mi-young's old wallet, containing a snapshot of her former beau adorned with numerous neck tattoos, painting a vivid picture of his rough exterior.
