Thistle is A Flower of Revenge

The second prince, Frederick, a mischievous fellow, learns that his maid, Thistle, was suddenly married as a concubine of a young new king in a neighboring country. Even though it was supposed to be a concubine situation, Thistle has been taken hostage in place of the royal family.

Frederick rushes to his father, the king, and finds out from his brother their father had committed unforgivable sins in the past that had ultimately led to the current situation. What will Frederick do to save his maid and exact revenge on this new king?