Mousetrap (2026): where to watch, cast and plot

About the series

The Rat (Korean: 들쥐) is a 2026 South Korean mystery thriller television series written by Lee Jae-gon, directed by Kim Hong-sun, and starring Ryu Jun-yeol, Sul Kyung-gu, and Lee Kyu-hyung. Based on the Kakao webtoon Field Mouse by Ludovico. It was released on Netflix on August 28, 2026.

Je Moon-Jae, a novelist who had one big success years ago, hasn’t left his apartment after being traumatized since his mother drove the car into sea killing herself and his father.

Agoraphobic and medicated Moon-Jae is content to let his college friend Son Su-Hyun run his entire life for him: bank accounts, prescriptions, even the deed to his own home.

That arrangement collapses the day his fingerprint stops unlocking his phone. Within hours he learns his apartment was sold out from under him, his identity documents were quietly re-registered by someone else two months ago, and a violent fixer named Noja, who believes Moon-jae vanished with money he embezzled three years back, is hunting him down. Cornered in an alley, Moon-jae comes face to face with the reason for all of it: a man wearing his own face.

Rather than staying enemies, Moon-jae and No-ja strike a deal ; No-ja will help find the impostor if Moon-jae repays the debt once his life is sorted out. It's an alliance of mutual leverage more than trust, and it drags both men into Seunggyu's world, a gangster running an identity-laundering operation that erases homeless and vulnerable people and repurposes their identities.

A detective named Park Sun-Yong is chasing a related thread: an unidentified woman's body pulled from the Han River, and an anonymous tip that keeps pointing him toward Moon-jae's address.

The deeper they dig, the more the story splits into two versions of the past. The official one, the one Moon-jae tells: a manipulative outsider named Yu-min wormed into his college writing club, stole his notebook, and later reinvented himself as "the Rat" out of envy. The real one: Yu-min was the actually talented writer. Moon-jae was the envious one. When Yu-min and Min-Young got together, Moon-jae destroyed her out of jealousy with anonymous rumors, driving her to suicide, then lifted Yu-min's unpublished work wholesale and built his entire career on it.

Yu-min sold his own identity into Seunggyu's laundering network, faked his death, had surgery to become Moon-jae's doppelgänger, and spent years methodically stepping into his victim's life ; his name, his money, his public image, while Moon-jae's guilt and mental illness made him an easy target to frame.

Moon-jae's parents once adopted a five-year-old and named him Moon-Jae, only to return him to the orphanage the moment they were able to conceive a biological son, to whom they gave the exact same name. That discarded child was Park Sun-Yong.

It all converges on a cruise ship, where Moon-jae finally corners "the Rat" and gets Yu-min's side of the story in full, followed by a fight that ends with Yu-min being pushed off the cruise into the sea.

Moon-jae’s editor hands him Yu-min's unfinished manuscript for a sequel that would name him as the real impostor if it's ever finished. He can't write a single line of it himself, the talent was borrowed all along and as guilt curdles into hallucination, he starts seeing Yu-min watching him from outside his window. The series closes on a knock at the door: Seunggyu, still owed his money, still out there.

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