Spoiler Warning: This article contains major spoilers for all 10 episodes of Netflix’s Mousetrap.
Netflix’s Mousetrap spends most of its story making us believe Je Moon-jae is the victim.
Someone steals his identity.
Someone wears his face.
Someone lives his life.
And Moon-jae desperately fights to prove that he is the “real” Je Moon-jae.
But the finale turns that entire idea upside down.
By the end, the most disturbing question is no longer:
Who is the Rat?
It becomes:
Did Moon-jae himself become the Rat?
The answer is essentially yes — but not because Moon-jae literally becomes Seo Yu-min.
Moon-jae becomes “the Rat” symbolically because the man who spent the entire series trying to escape an identity thief ultimately ends up trapped inside a stolen life of his own.
That is the final irony of Mousetrap.
The Rat Was Seo Yu-min — At First
For most of the mystery, the Rat is Seo Yu-min.
Yu-min was Moon-jae’s friend from the literary club.
He later changed his appearance and took over Moon-jae’s identity.
But the finale reveals something crucial.
Yu-min did not choose Moon-jae randomly.
Years earlier, Moon-jae had already taken something from Yu-min.
His writing.
Moon-jae used Yu-min’s ideas and notebook to build the literary career that made him famous.
Moon-jae also spread a damaging rumor involving Yu-min and Min-young, contributing to the tragedy that followed.
So Yu-min’s revenge is built around a cruel idea:
Moon-jae stole my work and my future, so I will steal his identity and his life.
That makes Yu-min the literal identity thief.
But Mousetrap does not stop there.
Moon-jae Was Never the Completely Innocent Victim We Thought He Was
This is the twist that changes how we understand the entire drama.
For much of the series, viewers experience the story through Moon-jae.
We see his fear.
We see his confusion.
We watch someone else apparently take everything from him.
Naturally, we sympathize with him.
But Moon-jae’s memory is incomplete.
Once the truth about his past emerges, the victim-versus-villain relationship becomes much more complicated.
Yu-min stole Moon-jae’s face and public identity.
But Moon-jae had already stolen Yu-min’s creative identity.
That does not make Yu-min’s revenge morally justified.
It does, however, destroy the simple idea that Moon-jae is merely an innocent man trying to reclaim what belongs to him.
Both men have taken something fundamental from the other.
Why Does Moon-jae Become “the Rat” in the Ending?
Because by the finale, Moon-jae has become trapped in almost exactly the kind of existence he feared.
He fought desperately to prove:
“I am Je Moon-jae.”
But what does being Je Moon-jae actually mean anymore?
His face?
His legal identity?
His books?
His reputation?
His memories?
The people who recognize him?
Almost every answer has become unstable.
Even worse, Moon-jae discovers that the career at the center of his identity was never entirely his.
When he tries to write again, he cannot.
That moment matters enormously.
Moon-jae spent years believing he was a writer.
But once Yu-min and the stolen material are removed from his life, he struggles to create anything.
The identity he fought so hard to recover suddenly feels hollow.
He got his name back.
But he no longer knows who the person behind that name really is.
The Apartment Is the Real Mousetrap
The final image of Moon-jae back inside his apartment is not simply the story returning to Episode 1.
It is the completion of the metaphor.
At the beginning, Moon-jae is a reclusive writer hiding from the world.
Then someone steals his identity and forces him outside.
He fights.
He runs.
He investigates.
He nearly dies.
He discovers the truth.
And after all of that…
he returns to the hole.
That is why the apartment feels like a mousetrap.
Moon-jae may technically have survived, but he has nowhere meaningful to go.
His identity is compromised.
His career is built on a painful truth.
The people around him have moved on.
And his past is still waiting outside the door.
He escaped the physical danger.
He did not escape himself.
Why Does Seung-gyu Call Him “Rat” at the Door?
The final doorbell makes the metaphor explicit.
Moon-jae is inside.
Seung-gyu is outside.
And Moon-jae is addressed as the rat.
The reversal is complete.
For most of the drama, Moon-jae was hunting the Rat who stole his life.
Now Moon-jae is the one hiding inside.
The hunter has become the hunted.
The victim has become the rat inside the trap.
That does not necessarily mean Seung-gyu knows every philosophical truth behind Moon-jae’s identity.
The importance is what the scene means to us as viewers.
Moon-jae has finally reached the position occupied by the very figure he spent the entire series chasing.
Why Does Moon-jae See Yu-min at the End?
Another deliberately ambiguous moment is Yu-min’s apparent appearance outside.
Moon-jae threw Yu-min from the ship into the sea.
So is Yu-min actually alive?
Mousetrap does not give us a definitive answer.
The figure can be interpreted in two ways.
1. Yu-min survived
The thriller interpretation is straightforward.
Yu-min may somehow have survived and could still be watching Moon-jae.
That possibility keeps the ending open.
2. Moon-jae is seeing Yu-min because of guilt
The psychological interpretation is arguably more important.
Yu-min no longer needs to physically exist to haunt Moon-jae.
Moon-jae now knows what he did.
He knows where his literary success came from.
He knows what happened to Min-young.
And he knows that defeating Yu-min cannot erase any of it.
In that interpretation, Yu-min has become part of Moon-jae’s mind.
Killing the Rat does not destroy the Rat.
Because the Rat now lives inside Moon-jae.
Why Can’t Moon-jae Write Volume 2?
This may be one of the most important clues in the entire ending.
Moon-jae finally has the opportunity to tell his own version of the story.
But he cannot write.
Why?
Because Mousetrap has spent the finale dismantling the identity of “Je Moon-jae, the successful novelist.”
Moon-jae’s success was connected to material that originated with Yu-min.
Once Moon-jae is forced to confront that fact, the blank page becomes terrifying.
It asks a brutal question:
If you remove everything Moon-jae took from other people, what remains?
That is why the inability to write is more than writer’s block.
It is an identity crisis.
Moon-jae recovered his legal identity but lost confidence in the identity he created for himself.
So Was Moon-jae the Real Rat All Along?
Not literally.
Seo Yu-min is still the person who carries out the elaborate identity theft and revenge scheme.
But thematically, the drama deliberately blurs the distinction.
Yu-min steals Moon-jae’s face.
Moon-jae steals Yu-min’s writing.
Yu-min takes Moon-jae’s public life.
Moon-jae builds his career from something that was not truly his.
Both men cross the boundary between “me” and “someone else.”
That is why asking who the “real Rat” is eventually becomes almost impossible.
The series begins by asking:
What if someone stole your identity?
It ends by asking:
What if the identity you were protecting was never completely yours in the first place?
Why Didn’t Moon-jae Get a Happy Ending After Everything He Survived?
This is one of the biggest frustrations viewers have expressed about the finale.
Moon-jae spends nearly the entire series suffering.
So after discovering the truth and surviving Yu-min, viewers naturally expect some kind of reward.
Instead, he ends up isolated again.
But that appears to be the point.
Mousetrap is not ultimately a story about Moon-jae defeating an impostor and returning to his normal life.
Because there is no normal life to return to.
The truth destroys it.
Moon-jae cannot simply become the man he was in Episode 1 because that man existed partly through denial, forgotten memories and a false understanding of his own success.
The adventure changed what Moon-jae knows about himself.
But knowledge does not automatically produce redemption.
Sometimes it simply makes the cage visible.
The Meaning of the Final Twist
The ending works because the “mousetrap” is not just a physical trap.
It is an identity trap.
Moon-jae spends the series believing that if he can prove his name, expose the fake and reclaim his life, everything will return to normal.
He succeeds in discovering the truth.
But the truth reveals something worse.
Getting his identity back cannot tell him who he is.
His name survives.
His apartment survives.
His face survives.
But his understanding of himself does not.
That is why Moon-jae becomes the Rat.
Not because he suddenly becomes the villain.
Not because Yu-min secretly wins in a simple sense.
But because Moon-jae ends the story hiding inside a life he can no longer fully believe belongs to him.
He chased the Rat.
He killed the Rat.
And then he discovered that the trap had been built around himself.
FAQ
Is Moon-jae the Rat at the end of Mousetrap?
Symbolically, yes. Seo Yu-min is the literal identity thief known as the Rat, but the ending turns Moon-jae into the “rat” trapped inside his own life and past.
Is Seo Yu-min alive at the end?
The drama deliberately leaves this ambiguous. Yu-min’s final appearance could mean he survived, or it could represent Moon-jae’s guilt and psychological collapse.
Why can’t Moon-jae write at the end?
His inability to write suggests that his identity as a successful novelist has collapsed after he learns how much of his career was connected to Yu-min’s stolen work and ideas.
What is Moon-jae trapped by?
Not just Seung-gyu or his enemies. He is trapped by his past, his guilt, his uncertain identity and the realization that reclaiming his name cannot restore his old life.
What does the final “rat” line mean?
It completes the reversal. Moon-jae began the series chasing the Rat who stole his identity. He ends the series hiding inside while someone outside calls him the rat.
Final Thoughts
The cruelest twist in Mousetrap is not simply that Moon-jae was hiding a dark past.
It is that he wins the battle he thought mattered — and discovers that winning does not save him.
He finds the man who stole his identity.
He learns the truth.
He survives.
But when everything is over, Moon-jae is back inside his apartment, unable to write and unable to escape the consequences of who he used to be.
The man who spent the entire story hunting a rat has finally become the one inside the trap.
And that may be the real meaning of Mousetrap.