The Treacherous (Korean: 간신; Hanja: 姦臣; RR: Gansin; lit.

Appointed as Chae Hong-sa, Im Sung-jae forcibly recruits beautiful women from across Joseon, calling them Unpyeong, seizing the opportunity to execute his grand ambition for ultimate power.

His ruthless actions, indiscriminately abducting noblewomen, commoners, and even the lower class, ignite public outrage.

To tighten his grip, Im Sung-jae and his father, Im Sa-hong, select the stunning Dan-hee for personal training, while the infamous courtesan Jang Nok-su, fearing her loss of influence, enlists Joseon's greatest gisaeng, Seol Jung-mae, to counter Dan-hee.

As treacherous courtiers engage in a fierce battle for dominance, Dan-hee and Seol Jung-mae must endure rigorous training to become the ultimate gi-saek and survive in a ruthless game of power and seduction.