The Violent Crimes Unit tackles an illegal gambling case, uncovering the MZ Union. Yubin forms the Dongbang Group to catch the leader.

Yubin's team goes undercover, gaining influence with a flashy social media account. Yubin secures a meeting with the MZ Union's right-hand man.

The body of a university student is found at Songnae Mountain. Yubin uncovers clues at the scene and the case mirrors the murder of Yubin's fiancee.