The undercover production team recently announced that "Actor Yeon Woo-jin, Han Sun-hwa, Park Doo-sik, Park Kyung-ri, Han Bo-bae, Yoo Sun-ho and Lee Jae-in have confirmed their appearance." They will add strength to the Drama following Actor Ji Jin-hee, Kim Hyun-joo, Huh Jun-ho and HGO who have completed the casting.
Undercover, based on BBC Drama of the same name, draws the story of Limited Express (Ji Jin-hee), a long-time informant who has been hiding his identity, and Choi Yeon-su (Kim Hyun-joo), a human rights lawyer who became the first head of the high-ranking public criminal investigation department (airborne). They protect justice and love against huge forces.
Han Sun-hwa plays Choi Yeon-su, playing Kim Hyun-joo's youthful days. Choi Yeon-su is the youngest person to pass the judicial examination at a prestigious university. Limited Express loves Choi Yeon-su, who has lived with this straight belief, with everything on the line.