Episode 4 of Shin’s Project kicks off with Mr. Shin engaged in a spirited yet futile attempt to snag a toy from a claw machine. After numerous failed attempts, a kind-hearted little boy steps in, offering his assistance. In exchange for his help, the boy requests a box of slime, and together, they manage to secure the coveted toy. With a triumphant smile, Shin then pays a visit to Si-on’s younger sister, Ye-on, and presents her with the toy as a gift. He gently requests that she keep their encounter a secret from Si-on. In a gesture of reciprocity, Ye-on shares a confidential piece of information—Si-on bears a cut on her arm and a bruise on her stomach, hinting at possible mistreatment by someone.
A flashback reveals that Philip had eavesdropped on the conversation between Shin and Jang Yeong-su the previous night. He is now aware that Shin had aided Lee Sang-hyeon and his mother in their escape. Meanwhile, in the present, Si-on takes Philip under her wing, teaching him the ropes of riding the delivery bike.
Once Philip resumes his duties at work, an unexpected visitor arrives at the store—an elderly gentleman named Park Myung-jin. Intrigued, Philip delves into some research and discovers that Park is not just any ordinary customer; he’s a corporate chairman with a staggering net worth in the billions. Moreover, he happens to be the landlord of the chicken shop!
Shin and Philip decide to have lunch at Pluto, one of the neighboring eateries. Over their meal, the owner, Mr. Jang, regales them with tales of a rude customer who had been complaining incessantly about Si-on. It turns out that Si-on is currently out on a delivery for this very customer—a man named Choi Yong-pal. In a malicious act, he drops the food on purpose and lodges another complaint with Mr. Jang. It becomes evident that Yong-pal is the culprit behind the stitches adorning Si-on’s arm. As she departs, he hurls threats in her direction.
Meanwhile, Choi Chul makes a comeback, reclaiming his former position as a detective. He ventures into a storage area brimming with case files and stumbles upon a notebook concealed in a crevice—presumably hidden by him years ago during his tenure as a detective. A flashback ensues, revealing Chul’s belief that Yun Dong-hee had been feigning intoxication on the fateful day he took little Jun’s life.
That evening, Shin insists that Philip accompany Si-on on her deliveries. At one of the stops, Yong-pal reappears, resuming his bullying tactics. It turns out that he had been a tormentor of Si-on’s in high school as well. This time, when he attempts to strike her, Philip intervenes, pinning Yong-pal down. However, they still need to be compensated for the chicken delivery. Thus, Philip sends Si-on home and heads back to the apartment, despite Si-on’s warnings about Yong-pal’s thuggish nature. At the doorstep, he has a change of heart and begins descending the stairs. But Yong-pal, seizing the opportunity, pushes him from behind, causing him to tumble down and lose consciousness.
Back at the store, the enigmatic man donning a hat pays a visit to Shin’s restaurant and places an order for food. However, Shin and Si-on soon sense that something is amiss when they fail to reach Philip. Concerned, Shin requests the mysterious patron to take the food home and promptly shuts down the restaurant. Meanwhile, Si-on catches sight of Yong-pal driving away in a car and decides to tail him. She follows him to a scrapyard, where she discovers Philip, bound and gagged in the trunk of a car, on the verge of being crushed. The operator, wearing headphones, is oblivious to Philip's desperate screams. Thankfully, Shin and Si-on arrive just in the nick of time to rescue him.
After the ordeal, Shin launches into an investigation and discovers that someone had deliberately turned off the CCTV cameras. With scant evidence to support a case of assault, the team is left with little recourse. Determined, they delve deeper into the matter. Shin pays Yong-pal a visit at his residence and gives him a piece of his mind, secretly recording their conversation. He then sends the recording to Kim Soo-dong, who skillfully manipulates it to create a fake recording of Yong-pal saying something entirely different.
Shin subsequently drops by Madame Joo’s abode to express his gratitude for her assistance in the Lee Sang-hyeon case. He then drops a bombshell, revealing that the mysterious man in the hat had a childhood photo of Ji-woo on his phone. He shows Madame Joo the CCTV footage, and she identifies the man as Kim Young-woo, Ji-woo’s father.
Meanwhile, as Si-on studies for her GED with Philip by her side, she confides in him about Yong-pal’s month-long harassment. She laments her helplessness, and Philip offers her a much-needed morale boost. Just as Philip is making plans for a dinner date with Si-on, Shin calls him.
Philip rushes back to the shop, where he finally confronts Shin about letting Lee Sang-hyeon go. Shin reiterates his reasons for sparing Sang-hyeon’s life. Just then, Kim Soo-dong arrives with more crucial information on the case. It turns out that Choi Woong-sik is Yong-pal’s father and also a councilman, vying for his fourth term. He is generally supported by Choi Eui-soo, a close confidant and the father of Yong-pal’s friend.
The following day, Shin pays a visit to Choi Woong-sik and recounts his encounter with a troublesome customer. With a determined look, he pulls out an audio recording device, unveiling the heated argument that had erupted between Si-on and Yong-pal. Not stopping there, Shin proceeds to play another recording—one that serves as incontrovertible evidence of Yong-pal's involvement in the attempted murder of Philip (most likely the fabricated audio clip ingeniously crafted by Soo-dong).
As the voices echo through the room, Choi Woong-sik's face contorts in recognition, the unmistakable timbre of his son's voice sending a chill down his spine. In a moment of resolve, Shin issues a stark ultimatum: if Choi Woong-sik wishes to extricate himself from this web of deceit, he must relinquish his political ambitions.
Yet, Yong-pal's descent into madness is far from over. Driven by an insatiable thirst for vengeance, he descends upon the chicken shop neighborhood, his eyes ablaze with a malevolent gleam. In a fit of rage, he sets Si-on's bicycle alight, the flames dancing merrily as they consume the innocent metal frame.
The episode of Shin’s Project concludes on a cliffhanger, with Philip and Si-on arriving at the scene, their faces etched with shock and disbelief as they take in the charred remains of what was once Si-on's trusted mode of transportation.
