Adrien must attend the Diamonds' Dance organized by his father and Mrs. Tsurugi. He will be the King of the Ball alongside Kagami, who has been chosen to be this year's Queen. Neither Adrien nor Kagami want to go, but they are only teenagers who cannot disobey their parents' orders. When she finds out that Adrien did not dare to tell her about the dance, Marinette decides to go too. But how will she enter such a private event where she does not seem to be welcome at all?