Episode 6 of "Gangnam B-Side" unfolds three years after the tragic demise of Jae-hee, with Dong-woo having abandoned his career in the police force without a word to anyone, now driving for a high-end escort service. A haunting flashback reveals Commissioner Moon's desperate attempts to dissuade Dong-woo, convinced that his departure stems from self-blame over Jae-hee's death and Ye-seo's disappearance.
Despite his newfound occupation, Dong-woo remains relentlessly investigative, stumbling upon a novel narcotic known as Neon in the hands of the Vice President's son, who had brutalized an escort. Dong-woo meticulously documents his findings, capturing a pivotal moment on camera: Su-in whisking away the injured escort.
Meanwhile, Gil-ho continues his relentless pursuit of K, who is incinerating batches of Neon. A startling revelation unfolds – the pimp has ascended to the directorial role at Gangnam Trading Company, orchestrating the mass distribution of Neon.
Prosecutor Min, having accepted Choi's proposition, now heads the anti-corruption department, hailed for resolving the mysterious Gangnam disappearances. A vocal YouTuber accuses her of corruption, yet she remains unperturbed, lacking concrete evidence against her. Dong-woo presents her with a Neon pill, but she brushes him off, refusing to apprehend the VP's son.
Elsewhere, Choi strives to propel Hae-il Tech's ambitious healthcare venture, Bio Town, amidst opposition from Tak, now the Presidential Secretary. With the President and the town's mayor, Woo, in his ear, Tak poses a formidable obstacle. Choi confronts Tak, who insists on his predetermined 30% cut from the failed Colosseum venture. Min secures Mayor Woo's favor by aiding his wife, leaving Tak furious and threatening to dismantle Min's career. Unfazed, Min swiftly arrests Tak on corruption charges.
In the meantime, Jang-ho locates Dong-woo and is disconcerted by his sudden silence. Relenting, Dong-woo unveils his clandestine probe into the dark underbelly of Gangnam. As for Ye-seo, she possesses Jae-hee's phone and texts him to steer clear while she attends to a critical matter. Jae-hee has been tailing her, noticing that Neon's presence coincides with her every online appearance.
That fateful night, Dong-woo discovers Su-in attending to Min-hee, the girl who first appeared in the episode, now gravely injured. As he whisks them to a physician, Gil-ho catches sight of them. Emerging from the shadows, he punches Dong-woo for betraying his pledge to safeguard Jae-hee. Dong-woo, burdened by guilt, bears the blow, which only fuels Gil-ho's rage further.
Gil-ho scolds Su-in for associating with the former cop, but she asserts it was Jae-hee's choice. Unconcerned with Gangnam's governance, she solely strives for survival. Elsewhere, Neon is widely distributed at a lavish party hosted at an academy, where Dong-woo and Gil-ho are invited as chauffeurs.
Concurrently, Jang-ho shadows Min as she heads to Hae-il Tech. Choi finally unravels his sinister scheme to plague the nation with Neon addiction and, through his Bio Town, present himself as the savior. This orchestration promises a perpetual, lucrative enterprise. He tasks Min with uncovering dirt on the food department, thus securing control over Neon's ingredients and its antidote.
At the academy, Ye-seo mingles with the VP's son, and the entire clique consumes Neon. Dong-woo arrives at the venue's periphery, startled to see her location. He dashes inside but encounters only a hush-hush disco party. In his frantic search for Ye-seo, he provokes a brawl, causing a disturbance. K phones Su-in to relocate the girls they've selected, prompting her to head to a room adjacent to the silent disco. She spots Ye-seo, who has regurgitated the drug, and trails her to her new destination.
