The third episode of "Gangnam B-Side" kicks off with an intense scene where the police discover Gil-ho's blade nestled beside the lifeless body of CEO Lee Gang-su. Meanwhile, Dong-woo confronts Prosecutor Min with accusations of siding with corrupt officers. In response, she demands concrete evidence proving that Captain Ju Yun orchestrated Gil-ho's demise. Frustrated and determined, Dong-woo informs Commissioner Moon of his intentions to assemble his own team, rendering Chief Prosecutor Tak's interference powerless to halt his pursuit of justice. He enlists Ji-su, and together, they track down the abandoned arcade, a place now void of its former vibrancy.
Elsewhere, Min advises Tak to redirect their focus onto another suspect, but Tak remains steadfast in his conviction to frame Gil-ho, who miraculously survived the perilous leap from the bridge. As for Noh Joon-seo, he has ascended to the position of CEO at the club, HYENA. When Min questions him about Gang-su's murder, he pretends ignorance and instead hands her Gil-ho's secret texting account, urging her to capture him as the perpetrator. He attempts to bribe her, but she disdainfully rejects the money. Instead, she delves into Joon-seo's past, uncovering a trail of charges against him, all of which were mysteriously dismissed by Tak. Her assistant, Mrs. Ryu, also uncovers crucial evidence: the blade contains Gil-ho's DNA.
Dong-woo's investigation leads him to the realization that the arcade once served as a base of operations for Madam Baek, now deceased. As he searches the premises, his eyes catch a glimpse of a business card belonging to Gangnam Trading Company. Ji-su, meanwhile, stumbles upon Jae-hee and Jung-hwa's social media profiles, revealing their friendship with Lemon. With newfound leads, Dong-woo heads to his hideout, and at the precise moment of his arrival, Gil-ho steps into the arcade, setting the stage for a dramatic confrontation.
He patches himself up, and a vivid flashback unfolds, depicting Baek, Gil-ho, and their female companions lounging around the base. They witness Jae-hee and Jung-hwa roughing up some recalcitrant clients who refuse to settle their debts. Impressed by their ruthless efficiency, Baek extends an invitation for the duo to join her ranks.
Gil-ho, serving as Jae-hee's chauffeur, keeps a watchful eye over her. Their bond deepens after hours, sharing drinks and dreams; Jae-hee dreams of retiring to a serene beach once she's amassed enough wealth. She notices the intricate tattoo on his wrist and requests a similar one to conceal her cigarette burns, a mark of her troubled past.
Tragedy strikes when Baek is brutally murdered over a monetary dispute. Jae-hee warns that the girls will now be compelled to seek refuge with other pimps. However, they place their trust in Gil-ho to safeguard them, and Jae-hee persuades him to carry on Baek's legacy.
Elsewhere, Min's mind reels with memories of Yun firing at Gil-ho during his daring leap. She revisits the crime scene, armed with subway CCTV footage, and stumbles upon Jae-hee, sitting on a bench adorned with flowers and sweets, lost in her thoughts. Just then, a call from Ryu shatters the tranquil moment, revealing that Gil-ho's DNA was also discovered on Jung-hwa's lifeless body. Jae-hee, startled by the mention of their names, bolts before Min can intervene.
Meanwhile, Dong-woo, accompanied by Jang-ho, treks to the Gangnam Trading Company building, realizing it's the same locale as Akira, the club they raided three years prior, now transformed into a glitzy hostess bar. Jang-ho uncovers drugs and confronts a gang of thugs, besting them all in a fierce brawl. Narrowly escaping a knife attack, he's rescued by Ji-su at the eleventh hour. Nearby, Dong-woo stumbles upon Lemon, busy filming drugged girls, and Yun, accompanied by an escort. Dong-woo apprehends them and subjects Yun to questioning, but he remains tight-lipped.
Tak, frustrated by the unresolved loose ends, pressures Min to pin the entire blame on Yun and bring the case to a swift conclusion. His temper flares when she suggests a thorough investigation, rejecting her proposal outright.
She poses inquiries to Yun, who proceeds to reveal that Tak stands as their ultimate authority. However, given that the chief prosecutor desires Tak's removal, Yun suggests she reach out to Joon-seo. Despite his hesitation, Yun somehow manages to send a distress signal to Joon-seo via text, but the young man, unfortunately, disregards it. Frustrated by the lack of response, Yun reluctantly agrees to negotiate with Min.
Determined to uncover the truth, Min confronts Dong-woo. She apologizes sincerely for her past mistake but confesses her intent to hunt down the genuine perpetrator. Dong-woo confides in her about Jae-hee, emphasizing the urgent need to locate her for the sake of his daughter.
Just then, Min receives a chilling call from Joon-seo. With a sinister tone, he reveals that Yun has been eliminated and Jae-hee is now in his custody, whom he intends to use as bait for Gil-ho. He issues an ultimatum, instructing both Gil-ho and Min to arrive by midnight if they wish to see Jae-hee alive. Gil-ho is thrown into a state of panic, while Min hastily informs Dong-woo about the existence of a covert messaging app.
As Gangnam B-Side Episode 3 draws to a close, a dramatic twist unfolds. Psyche presents Gil-ho with damning evidence – a figure cloaked in mystery, dressed in a crimson gown and adorned with an identical wrist tattoo. Joon-seo and his accomplices gaze at the image with malevolent glee.
