In Gangnam, a call girl flees her pursuers as Detective Kang Dong-woo, Broker Yoon Gil-ho and Prosecutor Min Seo-jin investigate a missing persons case.

A body at Gangnam Station prompts a Special Investigations Unit. Detective Kang reunites with Kim Jang-ho as Gil-ho suspects K-pop star Noh Joon-seo.

Dong-woo investigates with evidence from Gil-ho and meets an unexpected figure. Seo-jin seeks help as the case deepens while Gil-ho gets unsettling news.

Rescued, Gil-ho reveals the Colosseum is the key to the case. Jae-hee rushes to save her friend as Dong-woo and Seo-jin follow with their own motives.

Jaehee heads over to meet Choi Hakgu to save Yeseo, while Dongwoo and Gilho try to rescue Jaehee.

Seojin climbs the ranks with the help of Hakgu while Dongwoo becomes a chauffer and hunts for Yeseo.

Gilho returns to Gangnam seeking revenge for Jaehee and runs into Dongwoo who is looking for clues to find Yeseo. Madam Suin learns about Yeseo's dangerous plan and decides to risk her life to save Yeseo and other girls.

Jaehee's video is finally revealed, revealing the full story. Driven by love, revenge, and justice, every single one of them fight a battle against the cartel in their own way, for their own reasons.