Aired on the 10th, the fourth episode recorded a nationwide viewership rating of 3.3%, according to Nielsen Korea. In this episode, the trio of lawyers realized that a series of recent threats pointed back to a fateful day in 2005. Clues included the number '2005' scrawled on the rear window of Kang Shin-jae's (played by Jung Eun-chae) car, an attack on Yoon Ra-young (played by Lee Na-young) by a hooded assailant, and a vintage wine from 2005 sent as a gift at the L&J 10th anniversary event, all converging on a 20-year-old mystery.
Meanwhile, detective Gu Sun-kyu (played by Choi Young-jun) discovered that the first person to report the murder of journalist Lee Jun-hyuk (played by Lee Choong-joo) was his wife, Hwang Hyun-jin. This revelation sparked his suspicion that the L&J friends were hiding something together, bound by fate as accomplices. His suspicions deepened when he received an anonymous package containing a newspaper clipping about a 20-year-old disappearance case from Korea University's law school, where the L&J lawyers graduated. While investigating at the university library, he discovered that the stamp on Hwang Hyun-jin's hand symbolized the law school's academic club, Dike, and that the missing person was their fellow student, Park Joo-hwan.
At that moment, another victim of Connect-In, Han Min-seo (played by Jeon So-young), visited the L&J office. She revealed the app disguised as a home training app, explaining the system where VIP clients select options and pay in cash. The L&J trio was horrified by the scars left on Han Min-seo's body from the so-called 'lessons.' However, the app's server, code, and data were inaccessible.
The breakthrough came unexpectedly. Kwon Joong-hyun (played by Lee Hae-young), the second-in-command at L&J's parent company and Kang Shin-jae's mentor, visited to discuss establishing a public foundation. Han Min-seo, working part-time at L&J thanks to Yoon Ra-young, recognized the ring on Kwon's hand as belonging to someone present during her past ordeal. With Kang Shin-jae's quick thinking, Yoon Ra-young and Hwang Hyun-jin accessed the VIP client app on Kwon's phone, uncovering its horrifying reality. However, a security solution activated, deleting the app and sending photos of them to the server.
The recipient of this security alert was none other than Park Je-yeol (played by Seo Hyun-woo), the prosecutor in charge of the case of the deceased victim Jo Yoo-jung. The episode also revealed that forensic director Hong Yeon-hee (played by Baek Eun-hye) had swapped DNA samples with Yoon Ra-young under Park's meticulous planning. He pressured his wife, Hong Yeon-hee, with divorce threats, recorded calls, and monitored Yoon Ra-young, obtaining DNA results matching the suspect's blood from the 2005 case.
The episode concluded with a chilling overlap of past and present. Yoon Ra-young lay bleeding by the lakeside, while Hwang Hyun-jin swung a metal pipe to save Kang Shin-jae from being strangled, causing a man to fall into the lake.
The scene, which the three friends had recalled in nightmares with their current faces, transformed into their younger selves from 20 years ago. It was the face seen in the Korea University law school's mock trial victory photo that Gu Sun-kyu had found. The final piece of the puzzle, Park Joo-hwan's current face, was revealed to be Park Je-yeol.
Park Joo-hwan, presumed dead, stood before Yoon Ra-young as Park Je-yeol, with a sinister smile, saying, "It's been a while, I've missed you, Ra-young," extending his hand. Yoon Ra-young's eyes were filled with terror. The mystery of the 2005 disappearance, and Park Je-yeol's role as a prosecutor and Connect-In manager, left viewers questioning whether his motive was revenge or a warning to stop the investigation into the sex scandal.