Mousetrap wraps up its doppelgänger thriller in episode 10, and honestly, I went in expecting a clean villain-gets-caught ending. What I got instead was messier and, in some ways, more interesting: a finale that finally answers who’s really been pulling the strings between Moon-jae and the man calling himself the Rat, while leaving quite a few threads dangling on purpose. Here’s everything that happens in the last episode, plus my take on whether it sticks the landing.
How Episode 10 Opens: Moon-jae’s Memories Start Cracking Open
Mousetrap Episode 10 open on Moon-jae dozing off on a bus, and it’s here that his memories start leaking through again. He catches a flash of the day his schoolmates lived through a building fire, remembers a burnt sleeve, and jolts awake. It’s a small moment, but it sets the tone for the whole episode, everything from here on out is about memory, identity, and which version of the truth Moon-jae is willing to accept.
The Rat calls him not long after to ask if he got his flight ticket. Moon-jae confirms he did, but the Rat himself has other plans, he’s boarding a ship instead, and as he looks it over, he flashes back to a summer trip the two of them took on the very same vessel years earlier. In his head, he plays out how this all ends: Moon-jae standing in a house covered in blood, getting hauled away by police while the Rat watches from a safe distance in his car. It’s a chilling little preview of the endgame he thinks he’s engineered.
Detective Park Gets Back to Work Despite His Injuries
Meanwhile, at the hospital, Detective Park wakes up from treatment for his stab wound. His team fills him in, the old man, Hui-su, was last seen heading toward a children’s park. Park doesn’t hesitate. Injuries or not, he’s back on the case, insisting they need to track down Moon-jae immediately.
The Confrontation On The Ship
This is where things really kick into gear. On the cruise ship, a knock wakes the Rat up, and when he opens the door, Moon-jae is standing there with a knife pressed to his neck. “Hi, Yu-min,” he says, and just like that, the mask is off. It’s a genuinely great beat, the kind of confrontation the whole series has been building toward, and it doesn’t waste any time getting into it.
Back on land, Seung-gyu is packing a bag, clearly trying to get out of town, but he doesn’t have long. Noja shows up at his place within minutes. What follows isn’t pretty, Noja beats him badly and tells him that Dong-seok stole from the gang and paid for it with his life. Then Noja asks Seung-gyu a pointed question: if he lets him live, will he actually leave Noja alone? Seung-gyu’s answer is to stab him with a shard of glass, and Noja goes down.
Elsewhere, Detective Park and Min-ho head to the amusement park where Hui-su was spotted. A flashback shows Moon-jae’s parents there years earlier, holding a crying baby, with Hui-su watching them with visible worry, right before he loses sight of little Moon-jae and starts calling out for him in a panic.
Why Did The Rat Really Involve Detective Park?
Back on the ship, Moon-jae asks Yu-min flat-out why he’s done all of this. Yu-min’s answer is loaded: Moon-jae should already know why, he says, because Moon-jae isn’t even the real one. In the amusement park, Detective Park finds Hui-su sitting in the exact spot where a young Moon-jae once hid.
This is where the series drops its biggest reveal. Yu-min explains that he tipped off Detective Park because Park is the real Moon-jae, the one born first, who got sent back to the orphanage once the current “Moon-jae” was born into the family. Yu-min wanted the older brother to be the one who finally caught the younger one. It’s a gut-punch of a detail, retroactively reframing Park’s entire arc across the show.
The Real Reason Behind Yu-min’s Revenge
Yu-min’s motive, it turns out, is deeply personal. He wanted revenge because Moon-jae stole everything from him, his identity, his writing career, and Min-yeong, the woman he loved. According to Yu-min, after their trip together, Moon-jae started spreading vicious rumors about Min-yeong on the school forum. She dropped out, was cut off from her family, and her mental health deteriorated to the point that she attempted suicide.
Around the same time, Yu-min tried to sell his own writing, only to discover Moon-jae had already published it under his own name. Then came the worst blow of all.
How Did Min-yeong Die?
Min-yeong died by suicide. Yu-min came home that night to find her body, and while sitting with her, he read through all of Moon-jae’s published books and realized the man had essentially copied his entire life story. That’s the moment he decided to become Moon-jae and dismantle his life piece by piece. He also confesses to something else: he tattooed Min-yeong’s mark onto another person’s ankle, which is why the body pulled from the Han River was mistaken for hers.
Back at the hospital storyline, Noja gets medical attention and, in a surprising moment, calls Detective Park to ask him to save Moon-jae, since he says he can’t do it himself. Park seems to agree.
Does Moon-jae Actually Remember His Own Past?
Here’s where the episode gets genuinely disorienting, in a good way. The Rat realizes that Moon-jae has fully convinced himself of his own false version of events. Then it clicks for Moon-jae too, he finally understands why he’s had writer’s block for so long. None of the stories were ever his. The truth comes rushing back.
We see it all flipped from what we assumed: Moon-jae was working as a security guard when he saw a flyer for the inter-collegiate literature club. It was Yu-min and Min-yeong who were actually dating. It was Moon-jae who beat Yu-min up near the beach. And after that trip, it was Moon-jae who holed up in his parents’ house and started taking his mother’s pills.
So Who Is The Real Rat?
The full truth lands on Moon-jae: he is the real rat. Even Yu-min is thrown off balance by this, since his original plan was to frame Moon-jae at the beach and then disappear entirely, not to have Moon-jae figure everything out on the ship. When crew members start knocking on the cabin door, Yu-min decides someone has to die and reaches for the knife.
When the ship finally docks, Detective Park and his team are waiting. Moon-jae walks off flanked by security, calmly telling the detectives that “the imposter” attacked him and fell out the window during the struggle.
Is Moon-jae Pretending To Be The Rat’s Version Of Him?
Here’s a small but loaded detail: Moon-jae’s own personality shows through as himself, but he’s wearing the exact clothes the Rat always wore while impersonating him. In other words, Moon-jae is choosing to walk out as the “version” of himself the Rat had been presenting to the world all along.
Detective Park clocks this instantly and tells him to button his shirt all the way up, since that’s how the Rat always wore it. Then he asks the obvious question: why is Moon-jae still pretending? Moon-jae’s answer is that his mother always told him to be the best version of himself, and he finally understands what she meant. He also insists he never stole Park’s identity, he says he has always been Moon-jae. It reads as his way of shedding the insecurity that’s haunted his entire life.
What Actually Happened During The Fight On The Ship?
A flashback finally clears up the fight itself: Moon-jae is the one who stabbed Yu-min during their struggle. Before going down, Yu-min asks him if he still wants to be Yu-min. Moon-jae answers that he wants to be a better version of himself, and then throws him overboard.
Did Moon-jae Start The School Fire?
The fire that’s haunted this entire series finally gets its answer during a dinner between Moon-jae and Noja. Moon-jae tells him he doesn’t need his mother’s pills anymore, and as a result, his real memories have been resurfacing. He now knows, without doubt, that he started the fire himself.
He explains the pressure he always felt being compared to the “real” Moon-jae, and how he never truly felt loved by his parents. One day at school, he used a different name, and when his father found out, he berated him for it. The fire was Moon-jae’s way of trying to feel like someone else, if only for a moment, and of breaking every rule he’d been forced to follow.
Does Moon-jae Return Noja’s Money?
Moon-jae offers to give the money back, but Noja tells him it was never really his to begin with. He warns Moon-jae that Seung-gyu will absolutely come looking for it and tells him to stay hidden. Then Noja wishes him luck and walks away.
What Happens With The Rat’s Manuscript?
Han Ji-hye is eager to push out Volume 2 of “The Rat” and pressures Moon-jae to finish it. Moon-jae heads back to his old apartment and finds two boxes of cash waiting there. Going through Yu-min’s manuscript, he realizes it’s essentially a confession, hard proof that he himself is the true rat. He remembers Yu-min’s warning that the story wasn’t over yet.
Does Detective Park’s Marriage Survive?
During his divorce proceedings, Park asks his wife for one more chance, admitting that reconnecting with his uncle has made him reconsider what family really means. The show never shows us her response, leaving this thread deliberately open.
What’s Next For Noja?
Noja heads back to his hometown to live with his mother, seemingly settling in for a quiet life in the countryside. She wastes zero time putting him to work with chores, and he just smiles through it.
How Does Mousetrap End?
The finale closes on what plays like Moon-jae’s slow unraveling. He wakes from a nightmare where he’s being devoured by rats, then sits down to write Volume 2 of “The Rat.” He can’t manage to write himself an innocent ending, and Han Ji-hye’s messages only pile on the pressure.
Then the doorbell rings. He checks the security camera and sees an empty hallway. He looks out the window instead and sees Yu-min standing on the pavement below, staring right back up at him.
A beat later, the camera reveals it’s actually Seung-gyu at the door, demanding his money back. But Moon-jae can’t see him at all, he’s still fixated on the window, on Yu-min. He starts laughing, closes the curtain, and shuts himself inside.
My Honest Take: A Finale That Nails The Twist But Fumbles The Landing
Episode 10 closes out the doppelgänger storyline, and I’ll give it this: there’s real tension here, and the confrontation between Moon-jae and Yu-min delivers some genuine thrills. On paper, this finale had everything going for it, a great setup, a strong central mystery, and a twist that recontextualizes basically everyone’s arc.
It starts strong too. The buildup to the confrontation on the ship is tight, and I loved the twist of Moon-jae seeing through Yu-min’s plan and turning the tables on him mid-scheme. When the argument finally lays every card on the table, it hits hard, especially the reveal that Moon-jae had genuinely, sincerely forgotten the truth of his own identity. That confrontation feels like the only possible conclusion to the mess these two men spent the whole show creating together, and it’s easily the highlight of the episode.
Where it loses me is everything after. Moon-jae choosing to live as the version of himself Yu-min presented to the world, rather than as himself, or even as some reconciled mix of both, is a genuinely fascinating choice on paper. There’s so much to dig into there: does he actually believe the Rat’s version was the better one? Is this something that was always inside him, just waiting for permission to come out? The show never bothers to answer either question, which feels like a real missed opportunity given how much groundwork it laid.
I also can’t shake how much of a letdown it is that Noja never learns the truth about what Moon-jae actually did. Given how much screen time their relationship got, hearing Noja’s honest reaction, even if it was just him giving Moon-jae the dressing-down he deserves, would’ve added real weight to the ending. Instead, that whole thread just quietly fades out.
The Detective Park and childhood-brother reveal is another one that lands with less punch than it should, especially coming right after everything else the finale throws at us. After all those big swings, that particular thread feels almost like an afterthought rather than the gut-punch it was clearly meant to be.
But my biggest issue, by far, is that Mousetrap can’t seem to decide what it wants Moon-jae to be. The truth of his past paints him pretty clearly as the villain of this story, and that final scene, the laughing, the curtain closing, strongly implies things are about to go badly for him. And yet the episode never lets him sit in guilt, never lets him fully embrace being the bad guy either. He just kind of floats in the middle of it all.
Which, fittingly, is exactly where this finale ends up too.
