Set during the late Goryeo Dynasty, the King of Goryeo (Joo Jin-mo) faces political pressure from the Yuan Empire due to his lack of an heir, despite being married to a Yuan princess, the Queen (Song Ji-hyo). Secretly in love with his loyal commander of the royal guard, Hong-rim (Jo In-sung), the King devises a plan to secure his lineage: he commands Hong-rim to sleep with the Queen to conceive a child. What begins as a forced state duty turns into a passionate, secret affair between Hong-rim and the Queen, sparking jealousy, obsession, and deadly treason within the palace walls.