After finding out that Chloé has been blackmailing people from running against her as the class representative, Marinette decides to nominate herself for the position. Wanting to prevent Marinette from winning, Chloé organizes an autograph session by rock musician Jagged Stone to bribe her classmates into voting for her. When Marinette finds out about the autograph session and leaves her home to intervene, Chloé sends Sabrina to Marinette's home, in hopes of finding something humiliating which can be used against Marinette. Meanwhile, Mr D'Argencourt, Collège Françoise-Dupont's fencing teacher, has just lost the Paris mayoral elections by a landslide defeat. In anger and humiliation, he becomes influenced by Hawk Moth and turns into Darkblade, an armored black knight, who zaps people and knights them, transforming them into an army of armored knights to take over Paris.
This episode was first shown in South Korea on 17 November 2015 as episode 12