Mousetrap is a ten episode Korean thriller that arrived on Netflix on August 28, 2026, starring Ryu Jun-yeol and Sul Kyung-gu, created by Kim Hong-sun and Lee Jae-gon and based on the webtoon Field Mouse. It takes its title from an old Korean folktale in which a rat that eats a person’s discarded fingernail clippings can transform into that person’s exact likeness. Rather than turning this into supernatural horror, the show uses the legend as the engine for a modern story about identity theft, memory and revenge, and it becomes one of the more purely paranoid premises Korean television has produced in years.
The central figure is Je Moon-jae, played by Ryu Jun-yeol, a reclusive and celebrated novelist who lives an almost hermetic life in a luxury apartment in Seoul. His success came from a novel called Interview, published under the pen name Sung Hag-yun, which won him a prestigious Best New Writer award and launched his career. Since the death of his parents he has kept the world at arm’s length, structuring his days around tight routines and rarely leaving his apartment, with severe anxiety rooted in childhood trauma. His only real tether to the outside world is his friend and accountant Son Su-hyeon, who manages his affairs and effectively runs his daily life for him.
The story begins when Moon-jae’s fingerprint suddenly stops unlocking his own phone. His bank accounts reject him. His apartment does not recognize him. Su-hyeon, the one person who could vouch for him, disappears. Within days Moon-jae discovers that every system meant to confirm who he is has already accepted somebody else, a man who looks exactly like him, who has taken his name, his money, his home and his public identity. That man becomes known only as The Rat.
With nowhere else to turn, Moon-jae is forced into an uneasy alliance with Noja, played by Sul Kyung-gu, a calm and dangerous loan shark who runs a private investigation and debt collection operation out of his office. Noja has been hunting for Moon-jae for three years, ever since Moon-jae borrowed money from him and vanished, so his interest in finding the real Moon-jae is entirely mercenary at first: he wants his money back, and the Rat now sitting in Moon-jae’s life is the only lead he has. Their partnership is never comfortable. Noja is blunt, capable of real violence, and treats Moon-jae less like an ally than like a debt that happens to be able to walk and talk, and much of the show’s tension comes from never being sure whether Noja will protect Moon-jae or turn on him the moment it benefits him more.
Running alongside this hunt is Detective Park Sun-yong, a hardened police investigator who receives an anonymous tip pointing to a body pulled from the Han River, a tip that implicates Noja. As Sun-yong investigates the murder, he begins to notice the strange overlap between Noja’s case and the disappearance of the real Je Moon-jae, and slowly the three men, the imposter, the loan shark and the detective, are pulled into the same widening conspiracy, along with Park Seung-gyu, the boss of an identity fraud ring who has his own reasons for wanting Noja found.
For much of its runtime the show plays as a cat and mouse chase built on mistaken identity, in which Moon-jae has to somehow prove he is who he says he is while everyone around him, including the police, treats him as the fraud and treats the impostor as the real man. It is a premise that turns everyday bureaucratic facts, a locked phone, a rejected bank card, a database entry, into sources of genuine dread, because the horror here is not a masked intruder but the quiet, total erasure of a person’s legal existence.
The character work is where the show does its deepest damage. Moon-jae is introduced as a victim, a fragile genius whose isolation seems like the natural response to trauma and fame. Noja is introduced as a blunt instrument, someone whose menace seems purely functional. Sun-yong is introduced as a competent, slightly worn down cop trying to do his job in the middle of a case that keeps outrunning him. Each of these first impressions turns out to be incomplete, and the back half of the season is largely spent unwinding them.
The identity of The Rat is eventually revealed to be Seo Yu-min, a former friend of Moon-jae’s from their university days. The two of them, along with a young woman named Min-yeong, were part of the same intercollegiate literature club, and the true history between them is the emotional core the whole series has been hiding. In the version of events Moon-jae initially believes, he remembers himself as the wronged party in whatever happened between them. The real story, once it surfaces, is almost the exact opposite.
During a summer trip to Jeju Island, Moon-jae grew jealous watching Yu-min and Min-yeong spend time together. In a drunken moment he tried to confess his feelings to her, and she told him plainly that she and Yu-min had already been a couple in secret, long before Moon-jae had even met either of them. Moon-jae lost control and attacked Yu-min on the beach. Back in the city, consumed by envy and humiliation, he anonymously posted fabricated and sexually degrading claims about Min-yeong on an online forum. The rumor spread through their school, she was shamed by her peers, ostracized, and eventually dropped out and cut off contact with her own family, while Yu-min tried and failed to convince the police that Moon-jae had written the post.
As Min-yeong’s life fell apart, Yu-min stayed by her, supporting her emotionally and financially, and in an attempt to raise money for her he submitted his own unpublished manuscript, a novel called The Rat That Ate Fingernails, to a publisher. What he found instead broke him completely. That same story, his story, had already been published, under the title Interview, credited to the pen name Sung Hag-yun, which was Moon-jae. Moon-jae had stolen Yu-min’s unpublished work and built his entire literary career on it, the same career that had let him retreat into the comfortable, celebrated isolation the series opens with.
Not long after, Min-yeong died by suicide. Yu-min came home to find her body, and in his grief he sat and read through everything Moon-jae had ever published, only to realize that Moon-jae had not only stolen his novel, he had effectively rewritten their entire shared history, recasting himself as the sympathetic figure and Yu-min as the aggressor. That night is when Yu-min decided he would stop being himself. He underwent plastic surgery to remake his face into Moon-jae’s, trained himself to imitate Moon-jae’s voice and mannerisms, and spent years methodically dismantling the life Moon-jae had built, piece by piece, until he could walk into it and simply become him.
Part of that plan involved forcing Detective Sun-yong into cooperating by kidnapping his daughter, which is how the fabricated Han River murder gets tied back to Noja. Yu-min had also tattooed Min-yeong’s distinctive mark onto another woman’s ankle so that when a body surfaced in the river, investigators would believe it was her, deepening the frame being built around Moon-jae. Su-hyeon, the one person who might have helped clear things up early, dies by suicide before Moon-jae can get real answers from him, closing off what should have been the simplest route to the truth.
The series’ other major twist concerns Detective Sun-yong himself. As he digs into Moon-jae’s paperwork he finds an adoption certificate, and the investigation slowly reveals that Sun-yong was, in a previous life, also once named Je Moon-jae. He was the family’s original child, given up and sent back to an orphanage after a second child arrived and effectively replaced him under that same name, the child who grew up to become the novelist at the center of the whole story. Yu-min, once he learns this, deliberately pulls Sun-yong into the conspiracy because he wants the discarded older brother to be the one who finally catches the younger one who took his place, a piece of engineered irony that reframes Sun-yong’s entire arc, his difficulty forming attachments, his strained relationship with his own wife and child, as the long term cost of having been discarded as a boy.
By the time the truth comes out, Moon-jae’s own memory has been shown to be unreliable, distorted by trauma and by years of medication, so that the version of the past he believed in, the one where he was the injured party, was in many ways inverted from what actually happened. He was, in reality, the one who worked as a security guard and talked his way into the literature club pretending to be a university student, hoping to become, in his own words, a better version of himself. He was the one who beat Yu-min bloody on that beach. He was the one who destroyed Min-yeong’s life with an anonymous post. He was the one who stole the manuscript that should have been Yu-min’s. The show spends nine episodes letting the audience sympathize with a man who turns out to have manufactured his own victimhood.
The finale brings Moon-jae aboard a ship to finally confront Yu-min directly, in a scene that echoes the earlier ferry crossing the three of them once took to Jeju as students. Yu-min pulls a knife, the two men fight, and Moon-jae, in the grip of instincts he claims not to remember having, gets the upper hand and throws Yu-min overboard. When he comes ashore, Sun-yong is waiting to arrest him, but with one version of Je Moon-jae now dead, the surviving Moon-jae is able to let the blame for everything, the fraud, the kidnapping, the murder frame, settle on the man who can no longer speak for himself. He walks away technically free. The show does not treat that as a happy ending. Its final image is Moon-jae laughing to himself, a man who has survived and reclaimed his name and his fortune while having lost, by any honest measure, his sanity, his conscience and everyone who ever actually knew him.
What makes Mousetrap linger is that it never lets either man be simply the victim or simply the monster. Yu-min’s revenge is monstrous in its scale, kidnapping a child, faking a murder, years of calculated deception, and yet it grows out of a genuine, devastating injustice done to him and to Min-yeong. Moon-jae is undeniably a victim of an elaborate and cruel scheme, and yet the scheme only exists because of what he did first, and because he rewrote his own memory so completely that he could no longer recognize his own guilt. The series’ real subject turns out to be less about a stolen face than about how comfortable a false identity, or a false version of your own past, can start to feel once you have lived inside it long enough to believe it belongs to you.