Episode 10 of "Friendly Rivalry" kicks off with an intense encounter between Je-na and Je-yi, as Je-na urgently requests Seul-gi's father's contact details. Haunted by the conviction that their father, Tae-jun, committed murder after uncovering Seul-gi's forbidden liaison with her late dad, Je-na stealthily amasses incriminating evidence against him.
Elsewhere, Seul-gi is suddenly confronted with a grim sight—a corpse lying at Je-yi's father's clinic. There, she bumps into Tae-jun, who casually clarifies that the bodies are unclaimed individuals devoid of family or financial means, often serving as his practice dummies for surgical skills. He justifies his actions by claiming these unidentified corpses pose an unnoticed burden on district offices.
The following day, the tranquil atmosphere of the school is shattered by the arrival of detectives, who set out to interrogate all parties connected to a recent drug scandal. Seul-gi's name inevitably surfaces, and she is summoned for questioning. In a distressing twist, Beom-su fingers her as the culprit, heaping all accusations upon her shoulders. Separately, the detectives present Seul-gi with CCTV footage capturing her outside the pharmacy at Je-yi's father's hospital. Under pressure, Seul-gi reluctantly admits that Je-yi, not her, is the mastermind behind the drug operation.
Upon learning of Seul-gi's revelation, Je-yi is caught off guard. As Seul-gi confronts her classmates for singling her out, an unexpected alliance forms as Je-yi stands by her side. However, this fleeting moment of solidarity is shattered when Byeong-jin bursts into the school and whisks Seul-gi away. It transpires that Seul-gi had never consumed the painkillers from the hospital; instead, she had been hoarding them intended for Byeong-su. Savvy to the high school-run drug ring operating in their midst, Byeong-jin cunningly employs Seul-gi to place an order and surrender her social media profile, hoping to uncover the elusive dealer's identity.
Meanwhile, Je-yi slips through the cracks of police scrutiny, her father's influence shielding her from their probing eyes. When she confronts Tae-jun about his schemes against Seul-gi, he retaliates by casting a dark shadow of threat over her. Soon after, Je-yi uncovers Cho A-ra's deceitful plot to ensnare Seul-gi by feigning agreement to sell drugs through Seul-gi's social media profile and subsequently alerting the police. However, it transpires that Byeong-jin has been the puppeteer all along, manipulating events to coerce Seul-gi into a meeting at Gangnam Station to apprehend the fictional drug dealer.
Je-yi strikes a cunning pact with Je-na: in exchange for Je-na's presence at Gangnam Station, Je-yi promises to return her phone. Simultaneously, Je-yi orchestrates a sneaky maneuver, sending a covert message through Seul-gi's account, adeptly altering the meeting coordinates at the eleventh hour. Je-na, duped into believing the deal, complies and arrives at the intended rendezvous point, only to find a stash of drugs awaiting her. Seizing the opportunity, she snatches the contraband and dashes away, but Byeong-jin, mistaking her for the genuine dealer, gives chase, only to be interrupted by the timely arrival of the police. Meanwhile, Je-yi, with swift wit and resourcefulness, tracks down Seul-gi and aids her in a daring escape.
The episode concludes on a dramatic cliffhanger, with Byeong-jin frozen in horror as he witnesses Je-na being seemingly "abducted" by Tae-jun, the tables turning in a heart-stopping twist.
