The series revolves around , a meticulous judicial trainee who lives with his grandmother.

: He forms a tense partnership with Oh Soo-yeon , a successful businesswoman with a dark past seeking her own retribution, and Jang Sun-oh , a gambling genius who controls the prison's underground games. Cast & Characters

: At the suggestion of senior prosecutors, Yo-han goes undercover into Seongju Prison to gather evidence against a corrupt gambling ring and a high-ranking prosecutor.