Despite possessing all the power and wealth of the nation, King Yi In of Joseon is plagued by a profound sense of emptiness. "Kang Hee-soo," intent on overthrowing the King and seeking revenge, becomes a spy. In the midst of a fierce struggle for the throne, Kang Hee-soo's mission is to seduce Yi In and extract crucial information. Unexpectedly, she finds herself genuinely falling for the King. As their feelings deepen, a question arises: in this intense and merciless battle, who will ultimately prevail?