The apprentice knight, Lucas, spends his days being lectured by Valerie, the commander of the female knight order. He is always screwing up, but he has a dark side. He is an assassin. He is the eldest son of an assassin family who bury their enemies in the dark. But, one day, just before the outbreak of war with a neighboring country, he is forcibly married by his father. At their meeting, Valerie, the commander of a female knight order, appears. Despite their rejection of each other, they gradually become attracted to each other. However, what awaits them is a large-scale conspiracy over a secret royal family matter.