Episode 4 of "Study Group" kicks off with an intriguing backstory focusing on Lee-joon. Driven by his aspiration to become proficient in combat, he enrolled at Yusung Technical High School. Harboring a deep-seated desire to repay an elderly friend who once shielded him during his childhood, Lee-joon's path took a tragic turn when this very friend succumbed to the allure of gang life and eventually estranged him. Ironically, despite his fierce determination, Lee-joon proves to be woefully inadequate in the art of fighting.
His motivation for joining the study group stems from his yearning to learn combat skills from Ga-min. However, Ga-min sets a precondition: Lee-joon must agree to study if he wishes to be part of the group. To demonstrate his earnestness, Lee-joon readily concurs to undertake a math test while his peers visit Han-gyeong in the hospital.
As Lee-joon ponders over the test questions, an unexpected visitor, Jang-ho, approaches him, inquiring if he is Ga-min. Lee-joon, caught off guard, fabricates a tale and claims to be Ga-min, only to be whisked away by Jang-ho to a secluded warehouse. There, Jang-ho promises Lee-joon a car if he can pass the grueling Yeonbaek Gang initiation test. Unsurprisingly, Lee-joon fails spectacularly.
Meanwhile, Ga-min and the rest of the group return to school only to discover Lee-joon's absence. They scrutinize his test paper and marvel at his impressive performance, yet wonder about his whereabouts. Geon-yeob arrives with grim news: Lee-joon has been abducted by the gang.
Without hesitation, Ga-min, Geon-yeob, and Ji-woo spring into action, rushing to the warehouse to rescue Lee-joon, while Se-hyeon and Hee-won head to the police station to report the dire situation. Upon their arrival, they witness Jang-ho viciously beating Lee-joon for his deceit and failure in the test. A fierce battle ensues, with Ga-min once again employing his cunning tactics to deceive Jang-ho into underestimating him.
As Ga-min appears to be overpowered, Ji-woo's anxiety grows, fearing they may have bitten off more than they can chew. However, at a pivotal moment, Ga-min unveils his secret strategy, decimating Jang-ho in a ruthless display of strength.
Meanwhile, Detective Tae-man begins to harbor suspicions of corruption within the precinct. He ponders deeply on why Pi Han-ui was swiftly released without so much as a single interrogation, only to be dismissed by his superior to turn a blind eye. His concern deepens as he fears for Han-gyeong's safety, sensing that he is privy to the unsettling events that befell her a year prior.
Promptly after Hee-won and Se-hyeon relay Lee-joon's harrowing incident to the authorities, the police descend upon Jang-ho and his cohorts with swift precision. Tae-man, ever vigilant, hands his business card to the students, urging them to reach out should they find themselves in another bind. Yet, in a sudden twist, Geon-yeob dashes off to pursue one of the fleeing gang members who, in his haste, mentioned a haunting detail about his mother's demise.
As the turmoil at the school intensifies, Pi Han-ui continues to connive and scheme, plotting ways to further stir the pot. Parallel to this, the study group establishes their chat group, warmly welcoming Lee-joon into their fold. Days blend into one as they embark on their study sessions, fostering an unwavering bond of mutual support.
Upon her recuperation, Han-gyeong returns to the school, confronting the principal head-on for his negligence in overlooking Pi Han-ui's involvement. With resolve, she pens an official report detailing her findings. Subsequently, she gathers the study group students, enthusing them about an impending trip to another institution. She envisions this visit as an invaluable opportunity for them to learn and refine their study group dynamics, opting to take them to a prestigious school in Seoul.
Brimming with excitement, the students don their finest attire, eagerly anticipating the day of their journey. However, fate conspires against them when Ga-min arrives late, and Ji-woo, in a moment of oversight, sends him the incorrect name of the school.
