From the very beginning of Payback, Eun-yong (Lee Sun-kyun) has specified that the most sacred thing in his life is his relationship with his family. This doesn’t only include his blood family, but also his chosen family, which includes the CEO of Bluenet, Yoon Hye-rin (Kim Mi-sook), and her daughter Park Jun-kyeong (Moon Chae-won).
In a way, Eun-yong turned out to be half-decent in Payback, despite his ties to director Myung because of Hye-rin. She took him in, gave him a safe space to be himself, and nurtured him. So now that he has learned that the reason behind Hye-rin's death is his former boss and boss' son-in-law, prosecutor Hwang Gi-seok, things have taken a more serious turn in the K-drama.
Eun-yong agrees to Park Jun-kyeong's plan in Payback episode 4
When Park Jun-kyeong meets Eun-yong after years, there is no hatred. She doesn't hate him for not responding to her mails when her mother was in trouble.
This is because she understands his motivation and his choices. Instead, she only asks him not to stand in her way of revenge. She also says that she will not stop even if it means hurting Eun-yong's nephew Jang Tae-chun (Kang Yoo-seok).
Tae-chun is a rookie prosecutor in Payback, who dreams of joining the special investigation team headed by Gi-seok. However, he is serious about charging big criminals irrespective of their connections. So when his uncle offers him connections that he had never dreamed of, he accepts. He and Jun-kyeong come up with a plan that involves buying out a rich conglomerate that supports Director Myung.
Despite all the planning in Payback, things don't go as planned. When all of it backfires, Eun-yong agrees to a move that Jun-kyeong had planned from the very beginning.
She decides to come clean about the part that she had played in the case that had framed her mother as someone who had bribed a bank official. This will put an end to her career as a prosecutor in the military, and yet, she doesn't seem too bothered about that.
Eun-yong also agrees that this is the best course of action going forward. After all, he was a tad bit too careless in his plans in Payback, and this led to him almost getting killed by director Myung's men. If not for a friend -- Jin-ho -- Eun-yong would have very well lost his life. Jin-ho is the one who was tasked with killing Eun-yong, but an old debt stops the thug from doing so.
Now that the risks and stakes are higher, the question is how Eun-yong will outsmart the director. Not if, but how. After all, Eun-yong is the only person to have ever been successful in getting away from the director to start his own business.
He managed to outsmart him once in Payback, so a second time is not impossible. It would only be an uphill battle from here on for everyone who is related to Eun-yong in any manner in the K-drama.