Mousetrap

들쥐 ‧ Drama ‧ 2026

[SPOILER] WEBTOON PLOT SUMMARY

Cora Author

May 3, 2025 12:18 pm

Main Cast

Je Mun-jae: The protagonist. A former drama writer considered a guaranteed ratings hit. He currently runs a corporation under the alias "Cha Hyeon-u," with a Hong Kong subsidiary set up for tax evasion. He borrowed money from the loan shark Noja and fled. His success as a drama writer was actually built on stealing other people's work and registering it under his own name. His real writing ability is terrible.

Noja: A loan shark hunting Mun-jae for running away with his money. A complete monster, he has been known to dismember clients who don't repay him and process the remains into dog food.

Oh Gi-wan: "The Field Mouse." The central villain and most important character. He is the CEO of a charity called "Field Mouse House." In truth, this organization is essentially a pyramid scheme-like operation that murders people who abuse their social positions, steals their identities, and redistributes those identities to the poor, while also surveilling the people who receive those new identities. He is legally already dead, meaning Korean law has no way to process him.

Je Mun-jae 2 / The Doppelganger: A man sharing the exact same face and name as Je Mun-jae. He previously worked as a low-level employee at a cyber detective agency, monitoring people's personal information.

An Gyeong-hwan: Je Mun-jae's personal lawyer and middle school classmate. Despite appearing to help Mun-jae, he secretly conspired with the Field Mouse to replace Mun-jae with the doppelganger.

Na Seong-gi: Mun-jae's middle school classmate who speaks in a Gyeongsang dialect. In school he called Mun-jae "Jjanggoo." He was the one who told Mun-jae he had seen him at church, inadvertently giving Mun-jae the first clue about the Field Mouse. He later turns out to be a participant in the Field Mouse's plan, and Mun-jae tracks him down and confronts him in episode 19.

Kim Sang-su: A brutal middle-aged hitman with alopecia who speaks in a Chungcheong dialect. He is hired by the Field Mouse to eliminate everyone on a certain island who knows the Field Mouse's true identity. He routinely shoots corpses a second time to confirm the kill.

Park Sun-yong: A detective who is Mun-jae's middle school classmate. Demoted for assaulting a junior officer and stuck doing menial work, he is separated from his wife and children. He gets dragged into investigating the Field Mouse case after Mun-jae hands him a photo of the Field Mouse. Initially dismissive, he believed criminals acted from mental illness rather than environment, but after a lodging-house acquaintance's son commits suicide, he begins investigating in earnest.

Song In-ju: Mun-jae's former colleague and ex-girlfriend from his writing days. While walking away after meeting Mun-jae on his search for his own identity, she is struck by a car in a deliberate vehicular attack right in front of him.

Mun-jae's Uncle: An ordinary drunk in everyday life. However, he was deeply entangled in the Field Mouse's affairs, and was assassinated in a staged suicide just as he was about to reveal the truth to Mun-jae.

Part 1: The Man Who Hadn't Left in Ten Years

The Setup

Je Mun-jae borrowed money from loan shark Noja and ran. To avoid being found, he forged all documents under false names and fabricated records placing himself abroad. For ten years, he did not step outside for a single second. He handled all meals through delivery, exercise through a treadmill, and kept up with the world solely through the internet.

What we gradually learns is that Mun-jae's persona as a successful drama writer was entirely a fraud; he had submitted other ghostwriters' scripts under his own name, and his actual writing ability is terrible. His ten years of hiding were also partly due to this secret being exposed. He ran a corporation under the alias "Cha Hyeon-u" and managed all outside affairs through his lawyer, An Gyeong-hwan.

The First Clue: Something's Wrong Outside

One day, gazing at the street outside, Mun-jae notices that the same people have been wandering outside for all ten years. Then he hears from a classmate, Na Seong-gi, that someone who looked like him was spotted at a church. Sensing something deeply wrong, Mun-jae steps outside for the first time in a decade.

The Doppelganger

On this outing, Mun-jae encounters another "Je Mun-jae," a man with the exact same face and name as himself. This is one of the story's first major shocks. The doppelganger has been living as Je Mun-jae openly in the world while the real one hid inside.

The doppelganger's motive, revealed much later, is striking: he had worked at a cyber detective agency monitoring people's personal information, and one day came across Mun-jae's profile. He found it strange and also felt an odd inferiority toward this man who never left his house and had almost no social connections. Then he saw a cable TV broadcast of the folk tale "The Field Mouse That Ate the Fingernail," and it gave him the idea to copy Mun-jae's life entirely. Seeing the enormous digital footprint Mun-jae had left online, he put the plan into action. He was, in fact, one of the many ghostwriters whose work had been plagiarized and stolen by the real Je Mun-jae. He says that the real reason he became the "fake" was because a kind fake is better than a wicked original.

It also becomes clear that Mun-jae's own lawyer, An Gyeong-hwan, had been conspiring with the Field Mouse all along, the goal was to permanently replace the real Je Mun-jae with the doppelganger.

Part 2: Who Is the Field Mouse?

Part 2 is a deep, sprawling investigation spanning Mun-jae's middle school past. The central mystery: a dangerous, faceless figure known only as "the Field Mouse," identified by a tattoo on their left wrist reading SOTAE-91, who has been connected to a murder attempt on Mun-jae's life from years ago. Mun-jae teams up with reluctant detective Park Sun-yong and, unexpectedly, with Noja, the loan shark who had been hunting him, to unravel the truth.

The SOTAE-91 Tattoo

The tattoo "SOTAE-91" on the Field Mouse's left arm is first noted in episode 23, where Mun-jae recalls briefly seeing that inscription somewhere in his school days. He didn't recognize the Field Mouse's face among his classmates, but the inscription triggered his memory; that's why he pretended to know the Field Mouse when confronted. In Part 2, Episode 5, it is revealed that the Field Mouse is legally already dead, meaning Korean law has no way to touch them.

The meaning of "SOTAE-91" is only revealed at the very end: it is the address of Sotae Amusement Park, the place where the Field Mouse, as a child, was abandoned.

The Writing Club and the Middle School Murder Attempt

Mun-jae's investigation leads him back to his time at a school writing club. The key players are reconstructed:

Han Jung-pil: A manipulative classmate who tricked Mun-jae, who wanted to join the film club, into the writing club instead. He was the only student who shared a class with Mun-jae across consecutive years. When a writing assignment drew all attention to Mun-jae and left Han Jung-pil invisible, he spread rumors exposing other club members' secrets, and made plans to murder Je Mun-jae. This made him the prime suspect for being the Field Mouse.

The Reservoir Incident: Mun-jae's classmate Ko Ju-yong reveals that the victim of the SOTAE-91 reservoir murder attempt was Mun-jae himself. Ko had seen the SOTAE-91 tattoo on the Field Mouse's arm during their school days, which led to rumors that he was exchanging corpse photos with the Field Mouse.

Witnesses and testimonies: The school's livestock pen manager, Shin Yeong-tae, testifies that on the day of the reservoir incident, someone was coming and going from the pen and headed toward the school gate. The school's shooting range manager says that a gravedigger witnessed the scene at the reservoir, and that the culprit appeared to be a ghost. Former school disciplinary officer Oh Myo-han recounts the legend of the reservoir: a body covered in blood would float up once every ten years, explained by locals as the spirit of an orphan student unjustly killed during the Japanese colonial era. He says he doesn't believe it, and suggests Ko Ju-yong as a person connected to the culprit.

The Prison Visit: Han Jung-pil's True Motive

Noja had long suspected Han Jung-pil, since Han had vanished ten years prior. But he happened to see a wanted flyer: Han Jung-pil had been arrested for attempted murder and fraud and was already in prison. The Field Mouse's identity plunges back into mystery.

Mun-jae visits Han Jung-pil in prison. Han Jung-pil reveals that what Mun-jae thought was the motive was only the surface. The real reason was that Mun-jae had gossiped with club members about Han Jung-pil's mother. Han had claimed she was an insurance executive, but Mun-jae revealed she was actually a hostess at an escort agency. This humiliation was the true driver behind the murder plot. Mun-jae apologizes and internally says: "So in the end, it was I who drove you to try to kill me."

But the nature of Han Jung-pil's "attempt" is then undercut: the gunshot Mun-jae had heard was a firecracker placed inside a tree, and the flowerpot that fell on him was made of cardboard. Han Jung-pil had literally only planned, never acted. When Mun-jae presses him about the blunt weapon at the reservoir, the dead dog, and the ghost rumors he spread, Han falls silent, then, as he's led away, turns back and says with a meaningful look that he wasn't lying.

Later it's revealed that the "gravedigger" who claimed to witness a ghost at the reservoir was Han Jung-pil himself. After the incident became school news, he told classmates the culprit was the "reservoir ghost," but when no one believed him, he tried to convince himself he'd imagined it. He only realized the real culprit's identity later, when he saw a shooting club uniform on a fellow student, the same blood-soaked uniform he had seen at the reservoir. He also noticed the SOTAE-91 tattoo on that student's wrist. Too afraid to confront the person directly, Han anonymously reported it to the police, but nothing came of it.

Yi Geum-seok: Suspect, Then Victim

Yi Geum-seok's silhouette and hairstyle from school days matched those of the Field Mouse, making him a strong suspect. But in episode 47 he reunites with Mun-jae, clearing himself. His backstory is painful: his father was an undocumented Pakistani immigrant who was deported after being caught at an illegal gambling den. After being outed for confiding something about his sexuality following the writing club scandal, he joined others in tormenting Mun-jae. Consumed by guilt over his connection to the murder attempt, he reportedly died by suicide on a rock near the reservoir after entering high school. But in truth, he had been deeply entangled in the Field Mouse's affairs and was assassinated in a staged suicide just as he was about to expose the truth to Mun-jae.

The Island and the Assassination Campaign

In Part 2's latter half, a remote island is revealed as the Field Mouse's operational base, where people who know the Field Mouse's true identity are being systematically eliminated by hitman Kim Sang-su.

Organ traffickers who had been secretly cooperating with the Field Mouse's group while working for Noja are also killed by Kim Sang-su. In Episode 54, Noja seizes another hitman's gun to shoot Kim, but Kim shoots Noja in the ear first.

In Episode 63, Kim shoots Noja in the abdomen. In Episode 64, as Kim moves in to confirm the kill, the wounded Noja shoots Kim in the head with a gun taken from a police officer's clothing, killing him.

The Confrontation with the Field Mouse

In Episode 64, the Field Mouse finally reunites with Mun-jae and they fight in the next episode. The Field Mouse lures Mun-jae toward the entrance gate of Sotae Amusement Park, where Mun-jae shoots the Field Mouse. As the Field Mouse is dying, he hints at something staggering: the memory Mun-jae has always carried, of a crying child being abandoned by a father, is not a memory of himself. That crying child was the Field Mouse.

Part 3: The Full Truth

The Field Mouse's Real Identity: Oh Gi-wan

The Field Mouse's true name is Oh Gi-wan. His story is the emotional and moral core of the entire work.

He was a friendless orphan with no relatives. He was adopted into Je Mun-jae's family before Mun-jae was born. But once the biological child (Mun-jae) arrived, his adoptive parents' attention shifted entirely away from him. Mun-jae's father eventually abandoned Oh Gi-wan at Sotae Amusement Park. The tattoo "SOTAE-91" on his wrist was not a gang mark or code; it was the address of that amusement park, the place where he became an abandoned child.

After being abandoned, Oh Gi-wan was taken in by a man (listed in records as his father) who forced him to beg on the streets across different locations, and subjected him to physical and sexual abuse. He became so emotionally hollowed out he could no longer feel sadness. Then, on the last day he saw Je Mun-jae at school, something cracked open in him: he saw the way Mun-jae's father treated Mun-jae, which mirrored his own childhood trauma. He also read Mun-jae's writing assignment, an account of a childhood memory that felt identical to his own experience. He went back to Sotae Amusement Park.

The body that Mun-jae's old classmates thought they saw, a corpse in a school uniform, burned and unrecognizable, was actually Oh Gi-wan's abuser (the man who had taken him in), whom Oh Gi-wan had killed. Oh Gi-wan set the fire himself and killed that man. His school records show not "deceased" but "missing." This aligned with Han Jung-pil's testimony that Oh Gi-wan had vanished the semester after the reservoir incident.

The Shocking Childhood Memory Twist

An even more devastating revelation: the memory Je Mun-jae had always held of a young child crying as he was abandoned by his father, the memory Mun-jae believed to be his own, was actually Oh Gi-wan's memory. Mun-jae had somehow internalized it as his own. This had been foreshadowed throughout the story by the narrative note that "a person cannot see themselves in their own memories," because the child Mun-jae "remembered" was not him, it was Oh Gi-wan.

Oh Gi-wan's "Field Mouse House" Organization

Oh Gi-wan built and ran a charity called "Field Mouse House." In reality, the organization operates like a pyramid scheme: it targets people who abuse their social positions and power, murders them, steals their legal identities, and redistributes those identities to impoverished people with no records. The people who receive these new identities are then kept under surveillance by Field Mouse House employees.

In Part 3, Episode 3, Oh Gi-wan explains his reason for building this: as a child, he witnessed people at the very bottom of society dying as unregistered persons: people with no records, no family, no trace. He wanted to give them new lives. His intentions were good, but his methods were deeply wrong. The charitable activities and welfare facilities he built throughout the story, which we suspected were a cover, are revealed in the final episode to have been genuine.

Oh Gi-wan's Death and Aftermath

Oh Gi-wan had become a legal non-entity: no family, no registered connections, nowhere to anchor a life. Je Mun-jae was taken to Sotae Amusement Park. Oh Gi-wan, legally dead and everywhere at once, offered to sell Je Mun-jae his name back in exchange for the debt he still carried. In the struggle that followed, Je Mun-jae shot and killed him. After his death, with no next of kin, he was placed in an unregistered mourning hall as an unidentified person. The only people who remembered him were Je Mun-jae himself, and two former writing club members, Eu-tteum and Seong-pyo.

Aftermath:

Afterward, Je Mun-jae confessed his plagiarism and returned the money to the students he had stolen from. He wrote a new, original novel called People Without People. Field Mouse was officially remembered as an innocent victim. The welfare facilities he built continued to operate, benevolent on the surface and surveilled beneath. Hwang Tae-bok was arrested. Survivors like Kim Sung-pyo and Eu-tteum cooperated quietly. Lee Geum-seok visited Je Mun-jae and spoke of the outing, the guilt, and the suicide that followed.

Thematic Core

The title Field Mouse comes directly from the folk tale in which a mouse eats a human's fingernail clipping and takes on that person's face and identity. Every layer of the story reflects this:

The doppelganger literally becomes Je Mun-jae.
Oh Gi-wan was Je Mun-jae's "brother" before Mun-jae was born, then discarded. He spent his life haunting the edges of Mun-jae's existence.
Mun-jae himself had stolen the identities of ghostwriters to become a "successful writer."
Even Mun-jae's most personal childhood memory turns out to belong to someone else.

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