Mouse

Everything you need to know before you hit play.

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🔍 Psychological Thriller Pick

Mouse

마우스 (Mau-seu) · 2021 · South Korea

WriterChoi Ran

DirectorChoi Joon-bae, Kang Cheol-woo

Episodes20 eps · ~75–80 min each

Where to Watch✅ Viki, Prime Video

⏱️

Binge Time26h 40m

NetworktvN

AiredMar 3 – May 19, 2021

GenrePsychological Thriller · Crime · Mystery

Content Rating15+

Viki
Prime Video
Viu

Serial Killer
Nature vs Nurture
Police Procedural
Identity Twist
Psychological Mystery

One box. Everything you need to decide.

Lee Seung-gi and Lee Hee-jun lead a cast built around moral ambiguity — the show’s greatest trick is that the warmest person on screen is also its most dangerous.

Lee Seung-gi

Jung Ba-reum

Lead

Lee Hee-jun

Go Moo-chi

Lead

Park Ju-hyun

Oh Bong-yi

Supporting

Kwon Hwa-woon

Sung Yo-han

Villain

Kyung Soo-jin

Choi Hong-ju

Supporting

Woo Ji-hyun

Koo Dong-koo

Supporting

Spoiler-light recaps — enough to remember where you left off, nothing that ruins the ride.

EP 01

Pilot / First Case

March 3, 2021

Jung Ba-reum rescues a man from a violent assault before thinking twice about the cost — that instinct, immediate and unguarded, is what gets him assigned to Ko Moo-chi’s case. Mouse opens with a genetics lecture in its prologue: a doctor asks whether a psychopathic fetus should be terminated. Two couples are in the room. The episode answers nothing, but that prologue is doing structural work that won’t land until episode ten.

EP 02

The Test of Nature

March 4, 2021

Ba-reum and Moo-chi occupy the same investigation from opposite ends: one reads the crime scene through empathy, the other through accumulated grief that calcified long ago into something harder. The friction between them isn’t friction at all — it’s a gap the show is widening deliberately. What both of them miss, working separately, is more than either could have found working together.

EP 03

Patterns Appear

March 10, 2021

Bong-yi begins connecting dots that Ba-reum and Moo-chi were too invested to see clearly. Her approach is quieter — observation over reaction, evidence over instinct. The episode establishes her competence early because the show will need her reliable long before it tells you why.

EP 04

Questioning Identity

March 11, 2021

Evidence begins pointing toward Ba-reum’s past in ways that complicate his standing in the investigation. For the first time, the show asks the audience to hold distance from a character we’ve been asked to root for. The discomfort is deliberate — Mouse is testing whether sympathy survives scrutiny.

EP 05

Lines Crossed

March 17, 2021

Ko Moo-chi breaks procedure to extract information — a confrontation that slides into coercion — and then watches as other officers rationalize what they witnessed. Lee Hee-jun plays the aftermath with a specific blankness: a man whose moral vocabulary has worn down to the point where the word “wrong” no longer quite attaches to his own behavior. The episode earns that detail because it doesn’t point at it.

EP 06

Hidden Connections

March 18, 2021

New forensic evidence links several victims to a shared history that nobody had assembled yet — and the person who finds the pattern is Ba-reum. His immediate response is protective rather than investigative. The episode marks that distinction quietly and doesn’t explain it yet.

EP 07

The Past Returns

March 24, 2021

Childhood timelines surface — shared histories between suspects and victims that the adult investigation couldn’t account for until it went backward. The backstory revelations don’t answer the central question; they deepen it. Where a person comes from doesn’t explain who they become, and Mouse keeps making that argument while quietly arranging evidence for the counterargument.

EP 08

Trust and Doubt

March 25, 2021

The police institution officially doubts Ba-reum, which creates a different kind of pressure than the serial killer does — bureaucratic suspicion is intimate in a way that external threat isn’t. The episode watches Ba-reum submit to self-examination with an openness that should be reassuring. It’s the last episode where it fully is.

EP 09

A Closer Look

March 31, 2021

Moo-chi follows forensic threads that lead him somewhere personal — a crime that traces back to his own history. One of the show’s tighter procedural hours: less interested in theme than in watching a man work a case he is constitutionally unable to be objective about. The competence is real. The objectivity is not.

EP 10

Midpoint Revelation

April 1, 2021

Something happens to Ba-reum in this episode that changes everything he already was. The midpoint reveal lands correctly because Mouse spent nine episodes making you believe one thing so completely that the other thing doesn’t feel like a trick — it feels like the show finally telling you what you were already watching. Everything before episode ten now means something different.

EP 11

Lines of Evidence

April 7, 2021

The show has to manage something complicated now: the audience knows what the central characters don’t, and watching Ba-reum operate inside the investigation while concealing what he is requires Mouse to hold two emotional registers simultaneously. Bong-yi’s ethical clarity becomes the episode’s north — she is the only person in the room whose perception is still accurate.

EP 12

The Unexpected Suspect

April 8, 2021

An arrest brings the question of verification into focus: how much certainty is enough before acting? Characters who have been operating on gut certainty are put under pressure here, and some of them fail the pressure test in ways that will cost them later. The episode is Mouse being direct about the danger of conclusion without evidence.

EP 13

Fractures

April 14, 2021

Ko Moo-chi’s methods push against Bong-yi’s ethics at the moment the investigation most needs internal consistency. The cost of obsession shows up here — not as failure, but as the slow erosion of trust between people who are, separately, doing the right thing for the wrong reasons.

EP 14

Narrowing the Field

April 15, 2021

Separate timelines converge: victims, suspects, and witnesses turn out to have been adjacent for longer than anyone understood. Ba-reum’s compassion is still present in these scenes — and is now the most unsettling thing about him, because the audience knows what that compassion is covering.

EP 15

Truth’s Edge

April 21, 2021

The investigation breaks into territory protected by institutional power, and the show is direct about what that costs: Ba-reum pays a personal price that the episode refuses to treat as a plot convenience. The scene where the cost becomes clear is among Lee Seung-gi’s best in the series — it works precisely because you can no longer read it simply.

EP 16

Collisions

April 22, 2021

Direct confrontations between Moo-chi, Sang, and external figures bring loyalties into the open — characters who have been theoretical allies now have to act. The episode is Mouse at its most kinetic, not in physical action but in the velocity of decisions whose weight won’t be clear until the final episodes.

EP 17

Deepening Mystery

April 28, 2021

The investigation reaches a layer beneath the layer the team thought was the bottom. Bong-yi’s role expands from supporting observer to necessary agent — Mouse has been investing in her reliability since episode three, and this episode begins to pay that investment off.

EP 18

Penultimate Clues

April 29, 2021

Forensic links, witness statements, and personal revelations pull together in an assembly that places each major character within reach of a conclusion. The episode doesn’t rush. It’s Mouse doing its structural work — creating the conditions under which the finale will either earn or waste what the show has accumulated.

EP 19

Before the End

May 12, 2021

Ba-reum’s position inside the investigation becomes untenable — the distance between what he is and what the people around him still believe has closed to zero. Lee Seung-gi carries the episode with a stillness that is, by this point, more disturbing than any obvious intensity would be.

EP 20

Finale · Finale

May 19, 2021

Ba-reum’s crimes are exposed, the confrontation with Moo-chi arrives with the full weight of twenty episodes behind it, and Mouse answers its opening question without flinching. The ending doesn’t simplify. Ba-reum in prison, calm about what he’s become, is the drama’s honest admission that the genetic argument raised in the first scene was correct — just not in the way anyone wanted it to be.

Full spoilers ahead — everything that happens in the finale and what it all means.

What Actually Happens. Jung Ba-reum’s identity as the serial killer — the one Ko Moo-chi has been hunting through two investigations and twenty episodes — is finally exposed in full. The confrontation isn’t an ambush; it’s an assembly. The evidence, when it reaches Moo-chi, is complete and irrefutable: the murders, the manipulations, the gap between who Ba-reum presented himself as and what he actually did. What makes the scene remarkable is what Lee Seung-gi finds in it — Ba-reum faces the exposure without panic or denial, with a kind of clinical self-observation that the warm police officer in episode one could not have possessed. The warmth was real. That’s the thing the finale refuses to take back.

Is the Brain Transplant the Point? The mechanism behind Ba-reum’s transformation — receiving Sung Yo-han’s brain after the midpoint shooting — is the narrative decision that divides Mouse audiences most sharply. The show commits to it without apology: psychopathy was latent in Ba-reum’s DNA from birth (he is the son of serial killer Han Seo-joon), and the transplant removed the inhibitive layer that had kept that potential in check. This is the same genetic argument the drama opened with in its prologue. What the show is saying is not that the gene makes a monster. It’s that the gene, combined with the right conditions, removes the barrier between what a person is capable of and what they actually do.

Ko Moo-chi’s Resolution. Moo-chi gets accuracy, not catharsis. The killer he was hunting turns out to be the colleague he was partnering with — which closes a case without closing the wound underneath it. Lee Hee-jun’s final scenes are among his best in the series: a man who achieves exactly what he came for and discovers that achievement was never the point. The grief that made him a detective who hunts rather than investigates doesn’t disappear because the hunt is over. It was never really about the killer.

Oh Bong-yi’s Role. Bong-yi ends the drama as its most intact character — not because she escaped the damage, but because she built something that held when the people around her didn’t. Her refusal to let personal trust override evidence is what made Ba-reum’s exposure possible. Mouse needed her reliable from the beginning, and the finale pays that investment off: she doesn’t get to be surprised by the truth because she followed the truth regardless of what she wanted it to be.

What Mouse Actually Argues. The finale answers the opening question — can psychopathy be predicted? — with a yes that nobody wanted. Ba-reum had the genetic predisposition. He received the right brain. The conditions aligned. And the drama’s final image, a man in prison observing his own psychology with a calm scientific interest, is Mouse refusing to resolve that discomfort into something easier. He is not a monster the show invented to scare you. He is the answer to the question the doctors were arguing about in episode one, and Mouse is honest enough to let that be unsatisfying.