In Nine Puzzles Episode 4, the story takes a shocking turn as Kang Chi-mok is revealed to be the real victim, not the murderer. The episode begins with a mysterious and brutal crime involving a red suitcase, as the investigation pushes profiler I-na to confront her own dark reflections while tracking down a manipulative killer hiding in plain sight.

The episode opens with Chi-mok angrily banging on a hotel door before the scene cuts to a brutal murder. A man is killed, dismembered, and his limbs are packed into a red suitcase. The killer, dressed like Chi-mok, disposes of the suitcase in a lake. The next day, police begin searching for Chi-mok and find his abandoned car at a rest stop. CCTV footage shows someone in Chi-mok’s clothes walking away at 3:17 a.m. Han-saem climbs over a boundary wall nearby and scrapes his hands, believing Chi-mok faked his death after killing Mi-young.

I-na, however, thinks differently. She profiles Chi-mok as short-tempered and impulsive—traits opposite to the calculated behavior of the suitcase killer. Meanwhile, Seo Yang-hee, Chi-mok’s wife, claims he never returned home, but surveillance shows otherwise. He drove to Yeongpyeong Reservoir and stayed at a nearby love hotel. There, Han-saem finds blood in the sink. Guests had reported loud music around 2 a.m., and a man in Chi-mok’s clothes was seen leaving with the red suitcase.

The suitcase is recovered from the reservoir, and forensics confirm it held a dismembered body. I-na deduces that the killer likely tased the victim from behind. The victim had no signs of struggle and matched Chi-mok’s DNA. I-na argues that the gloves worn while driving his own car, and the flawless disappearance, point to a misdirection by a second person.

Nine Puzzles Episode 4 reveals Yang-hee’s past and manipulative nature

As I-na digs deeper, she learns from the housekeeper that Dong-hoon changed after discovering I-na was orphaned. This information haunts I-na, who later tells Dr. Lee she has trouble sleeping—guilt over not stopping Dong-hoon’s killer. Meanwhile, Chi-mok’s credit card shows he booked a hotel room the same night he disappeared, which matches the location of the murder.

Back to Yang-hee, I-na pays her a visit and bonds with her over music and shared past trauma. Yang-hee admits Chi-mok once gave Mi-young an expensive apartment and regretted it. She talks about needing her own bedroom due to her history of living with family until they died in a house fire. I-na sees herself in Yang-hee—both orphans with repressed emotional responses. But this only makes her more suspicious.

I-na shares a new theory with her team: someone impersonated Chi-mok to divert attention. The motive? Someone wanted him gone, permanently. The profiler suspects Yang-hee. Han-saem confirms Yang-hee lied—Chi-mok did go home, caught on video. But when I-na tries to discuss it, Han-saem ignores her, so she breaks into his apartment and points out Yang-hee’s detached reaction to her husband’s death. Han-saem says I-na herself didn’t cry when Dong-hoon died.

Yang-hee is brought in. She abruptly shifts blame to her lover, Roh Jae-wook. When Han-saem interrogates him, Jae-wook claims Yang-hee was miserable in her marriage but has visible scrapes on his hands—matching the rest stop evidence. I-na and Han-saem split the suspects and use a psychological trap to make them turn on each other.

During her chat with Yang-hee, I-na casually reveals she owns the same red suitcase. Yang-hee’s expression falters. Meanwhile, Han-saem tells Jae-wook about Yang-hee’s tragic past, where a friend was blamed for a fire that killed her grandmother and sister—then that friend mysteriously vanished. Jae-wook panics, realizing she could do the same to him. He confesses, leading police to Chi-mok’s head.

The case seems closed. The media announces Chi-mok killed Mi-young and was then murdered, removing pressure from the police. I-na brings her team baseball caps as gifts, though it’s clear she’s obsessed with the image of Dong-hoon’s killer—who also wore a cap. She insists Chi-mok didn’t kill Mi-young, and Han-saem is intrigued.

Dinner with Dr. Lee ends the episode on a more personal note. I-na worries she might be manipulative like Yang-hee, but Dr. Lee assures her she is honest and self-aware. The episode concludes with I-na receiving a new puzzle: a photo of a dismembered man wearing an armband, surrounded by children.