Episode 3 of "Study Group" kicks off with Han-gyeong inquisitively probing about Pi Han-ui, only to be met with a stark warning to cease her investigations into him. Her hesitant informant solemnly cautions her that delving into Pi Han-ui's affairs could very well spell her doom. To everyone's astonishment, Pi Han-ui himself decides to make an unexpected appearance before Han-gyeong.
Meanwhile, Ga-min and Se-hyeon find themselves on a mission to uncover the identity of Ji-woo and the reasons behind her desire to join the study group. The revelation comes as a shock: Ji-woo is none other than Hyeon-wu's twin sister, yet she had not applied for the study group herself. Her loyal best friend, Hee-won, had taken it upon herself to apply on Ji-woo's behalf, hoping to shield her from bullies. Tragically, a malevolent individual named Gyu-jin had filmed Hyeon-wu committing a store robbery and has been using this footage to coerce Ji-woo into submission. Worse still, Gyu-jin had deceived Hyeon-wu, robbed him, and framed him for a loan. Unaware of Gyu-jin's treachery, Hyeon-wu, believing himself to be the victim of a robbery, approached Gyu-jin for a loan.
Upon spotting Ji-woo and witnessing Gyu-jin and his girlfriend bullying her firsthand, Ga-min is compelled to intervene. Hee-won, desperate for help, also pleads with him, assuring him that Ji-woo will join the study group if their tormentors are dealt with. Determined to assist Ji-woo, Ga-min embarks on a perilous mission to confront the disciplinary committee. According to Se-hyeon, the disciplinary committee resembles a school-sanctioned mafia, with no one daring to cross them. Se-hyeon fears that Ga-min is embarking on a suicidal mission, yet he reluctantly agrees to help.
Ga-min stealthily infiltrates the disciplinary committee's office and discovers two other boys searching for the blackmail video. Gyu-jin catches the nosy boys and brutally beats them up before deciding to upload the video online. Hearing this, Ga-min is forced into action. He emerges from his hiding spot and engages in a fierce struggle to secure the USB. He cleverly deceives Gyu-jin into believing he is stronger and endures several punches to grab the USB. Once he has the USB in his possession, he beats Gyu-jin and makes his escape. Unfortunately, the other members of the disciplinary committee arrive before Ga-min can flee. Another intense battle ensues, leaving Se-hyeon and Hee-won worried that Ga-min is being overwhelmed.
As Ga-min confronts the disciplinary committee members, Hee-won and Se-hyeon frantically brainstorm a plan to lend him a helping hand. Unbeknownst to them, Ji-woo, who has been keeping a low profile for her brother's sake, overhears their conversation and is incensed that she was kept in the dark. She decides that she has had enough of playing the weakling.
Elsewhere, Han-gyeong meets with Pi Han-ui in an attempt to persuade him to spare Hyeon-wu. As anticipated, Pi Han-ui stubbornly refuses to take any responsibility and warns Han-gyeong to drop the matter. However, Han-gyeong stands her ground, intriguing Pi Han-ui with her perseverance.
Back at the disciplinary committee, Gyu-jin realizes that the incriminating video has already been uploaded to his hard drive and prepares to share it. In a bid to stop him, Ga-min swiftly snatches the hard drive and dashes away. Se-hyeon and Hee-won trail closely behind, puzzled by his actions. Inevitably, Gyu-jin and his cronies give chase.
Ga-min stumbles over some wires, causing the hard drive to clatter at Se-hyeon's feet. Se-hyeon snatches it up and races to the rooftop, where he manages to destroy the hard drive by hurling it over the edge. Alas, Gyu-jin catches up to him just as Ji-woo steps in, delivering a beating that Gyu-jin will never forget.
Meanwhile, Ga-min accidentally lets the USB slip from his grasp, and Hee-won makes a desperate lunge for it. However, Mi-hee, one of the bullies, beats him to it. This time, Hee-won refuses to be intimidated and attacks Mi-hee to reclaim the USB.
Their triumph is fleeting, however, as Hyeon-wu arrives on the scene, fueled by Pi Han-ui's revelation that Gyu-jin betrayed him. Pi Han-ui arms Hyeon-wu with a knife and goads him to kill Gyu-jin. Hyeon-wu arrives at the school with murder in his heart, but Han-gyeong steps in and is stabbed in the process. As she slumps to the ground, Han-gyeong vows to help Hyeon-wu.
The students stand in collective disbelief as the unfolding drama captivates their attention. Ga-min, driven by urgency, scoops up Han-gyeong and rushes her to the hospital without delay. Following the tense surgery, Han-gyeong, her spirit unbroken, extends a warm welcome to Ji-woo and Hee-won, inviting them into the fold of their study group. Ji-woo, though saddened by the circumstances that have strained her bond with her brother—a relationship built on mutual dependency—acknowledges that he has crossed a line.
The next day dawns with a renewed sense of purpose as Ga-min and the study group members convene for their inaugural meeting. Ga-min's excitement is palpable. Concurrently, the police summon Pi Han-ui for interrogation, though their custody of him is brief and unfruitful. The episode culminates in a dramatic turn as Tae-oh, another student, vows to make war on Ga-min after being regaled with tales of his legendary battles. Initially indifferent, Ga-min's interest piques when Tae-oh's henchmen bring forth Lee-joon, a hopeful aspirant for the study group whose application Tae-oh callously tears apart. Incensed by this act of defiance, Ga-min, in a burst of fury, leaps from the third-floor classroom window, descending with the grace of a hawk to deliver a devastating knockout punch to Tae-oh, leaving him momentarily unconscious.
