Mousetrap Episode 4 is the hour where the show finally hands us a name for its shadowy puppet master, The Rat, and honestly, I don’t think I exhaled once during that final ten minutes. If you’ve been waiting for Moon-jae’s world to fully collapse, this is the episode that lights the match. Below is a full breakdown of everything that happens, followed by my thoughts on where the story is headed.
How Episode 4 Opens: The Lakeside Trap
Mousetrap Episode 4 kicks off with Soo-hyun showing up by the lake and calling Moon-jae’s phone. Moon-jae, in a move that made me want to yell at my screen, calls out to him and actually runs toward him instead of staying put. Soo-hyun immediately gets back in his car and speeds off. Noja and Moon-jae take off after him, and Detective Park, never far behind, follows the both of them.
What follows is a genuinely tense highway chase. While he’s driving, Soo-hyun gets the doppelganger on the phone and accuses him of setting a trap. He reminds the doppelganger of a promise — that Moon-jae said he’d let “her” go if Soo-hyun did everything that was asked of him. The doppelganger doesn’t budge. Instead, he forces an impossible choice on Soo-hyun: his own life, or his daughter’s.
Meanwhile, Detective Park’s part in the chase ends abruptly when Seung-gyu’s car T-bones him.
Soo-hyun’s Confession Above the Han River
Soo-hyun picks his daughter, obviously, and steers his car toward a broken bridge. The crash leaves him standing at the edge, overlooking the Han River, and this is where the episode really opens up. He tells Moon-jae that the doppelganger goes by the name The Rat, and that this man approached him a full year earlier already knowing everything about the investment funds Soo-hyun and Moon-jae had stolen together. The Rat used that knowledge as leverage, threatening Soo-hyun until he handed over Moon-jae’s phone so it could be hacked.
From there, things got darker. The Rat kidnapped Da-eun, Soo-hyun’s daughter, and used her as insurance to force Soo-hyun into carrying out everything that’s happened over the past several days. Soo-hyun swears he doesn’t actually know why The Rat is doing any of this, but he says The Rat was very clear that Moon-jae would know exactly why. He looks Moon-jae dead in the eye and accuses him of lying.
A flashback interrupts here, cutting back to the moment Soo-hyun and Moon-jae reunited after high school. Even back then, Soo-hyun noticed something had changed in Moon-jae. It’s a small detail, but it’s the kind of breadcrumb this show loves to drop.
Detective Park Hits a Wall, Seung-gyu Makes His Move
Back in the present, Moon-jae wonders out loud whether he should just go to the police with everything. Noja shuts that down fast, without hard evidence, no one’s going to believe a word of it.
Over at the station, Detective Park is butting heads with his boss. He’s got nothing solid to work with, and it’s putting him on edge. Meanwhile, at the gambling den, Seung-gyu has his crew churning out fake IDs, and he tells them to start scouting for new “bodies” to exploit.
The White House Discovery
Moon-jae and Noja head back to the office and find the door unlocked, which is never a good sign in a show like this. Inside, they discover a piece of paper listing the address of a white house, the place where The Rat had been keeping Da-eun. They rush over and find her locked in one of the rooms.
Detective Park’s team gets pulled into the case almost immediately after. When they arrive at the same house, another officer shows Park photographs of their prime suspect: it’s Noja.
Driving away, Moon-jae realizes just how deep the hole they’re in actually is. Da-eun can identify him as her kidnapper, and that automatically makes Noja a suspected accomplice. Sure enough, that’s exactly the conclusion Detective Park’s team reaches, and they’re soon in pursuit of both men.
A Narrow Escape and a Flash of Memory
Noja starts packing cash and supplies to go into hiding, but the moment they step outside, they spot Park and his team waiting. They scatter and run, get separated in the process, and Moon-jae nearly gets caught. When Park punches him during the struggle, something strange happens, Moon-jae has a flickering vision, almost catching a glimpse of the real face hiding behind The Rat. He comes to just in time to watch Noja knock Park unconscious.
The two hole up in a hotel room afterward. Standing in front of the bathroom mirror, Moon-jae sees fragments of The Rat’s true face again. It’s brief, disorienting, and clearly meant to keep us guessing.
The next morning brings grim news: Soo-hyun’s body turns up floating in the water.
Seung-gyu Closes In On Noja
At the same time, Noja runs into Seung-gyu, who’s waiting for him with two of his men. Seung-gyu claims to be an old associate of Dong-seok, the man Noja killed, though Noja plays dumb and pretends not to recognize him. It turns out someone tipped Seung-gyu off, telling him that Noja betrayed Dong-seok and made off with money that Seung-gyu believes is rightfully his.
Back at the hideout, while Noja and Moon-jae are packing to leave, someone rings the bell. It’s a man in a hat who hands Moon-jae a phone and instructs him to hit speed dial 1. He does, and finds himself talking directly to The Rat for the first time. The Rat’s message is simple and chilling: find yourself, and you’ll find out who I am. He tells Moon-jae to hurry before cutting the call.
The Suspicious Lunch and That Cliffhanger Ending
At the morgue, Detective Park studies Soo-hyun’s body and suddenly remembers Moon-jae shouting his name back at the lakeside, a memory that clicks a few pieces into place for him. He then tracks down Byeong-jun to ask about Noja, and Byeong-jun tells him about a gang that gets people trapped in debt so they can sell off their identities, before hurrying away.
Elsewhere, Seung-gyu enlists Myeong-su to help track down Noja and clean up the mess drawing so much police attention. Since Seung-gyu was the one who set Myeong-su up with a new identity back when he was on the run from the cops, Myeong-su doesn’t really have a choice but to comply.
Over lunch, Moon-jae finally tells Noja that he thinks he’s figured out who The Rat is. A flashback shows him on a beach with a man named Yu-min. Back in the present, Moon-jae says he suspects it’s a college friend who used to be envious of him, though the way he says it feels like there’s more to the story.
As they leave the restaurant, it turns out The Rat was there too, sitting somewhere in the same room. He pays with a card that triggers a text alert straight to Noja’s phone, which goes off just as Noja gets into the car with Moon-jae. The instant he realizes something is wrong, two men hiding in the backseat attack them, and the episode cuts to black.
Episode 4 Review: A Slower Build With One Explosive Payoff
Episode 4 is honestly a mixed bag for me, and I think that’s an important thing to say plainly rather than pretend every hour of this show is firing on all cylinders. The central thread between Moon-jae and The Rat is still the strongest thing this drama has going for it, especially now that we finally understand how The Rat manipulated Soo-hyun into becoming his instrument. The name itself, The Rat, carries so many possible meanings, and the fragmented flashbacks Moon-jae keeps experiencing only deepen the mystery rather than resolve it. When he tells Noja that half-truth about a college friend named Yu-min, my first instinct was disbelief. Who actually is Yu-min? What did Moon-jae do to him? And, maybe the bigger question lurking under all of it, is Moon-jae even who he thinks he is?
Noja and Moon-jae’s dynamic keeps working, too, largely because Noja is quietly carrying this entire mission on his back while Moon-jae fumbles through most of it. It’s almost darkly funny how helpless Moon-jae is without him at this point. But that helplessness raises a real question worth sitting with: could this be the kind of person who did something terrible enough to deserve a revenge plot this elaborate?
Where the episode loses me a bit is with Detective Park’s storyline. The constant friction between him and his team doesn’t seem to be building toward anything meaningful yet, and it starts to feel like noise rather than tension. I felt the same way about Seung-gyu and Myeong-su’s scenes tied to Dong-seok, we simply don’t have enough context about these characters for their conflict to land emotionally. The money Noja allegedly owes them also arrives so suddenly that it reads more like a plot device than an organic development.
Still, credit where it’s due, the episode does successfully raise the stakes, and that final cliffhanger is legitimately thrilling. Mousetrap continues to be at its best in these closing-minute gut punches, and Episode 4 delivers one that’ll have you hitting play on the next episode immediately.
Mousetrap Episode 3 | Mousetrap Episode 5
