Catalyst (Heroes' Day - Part 1)

It's the Day of Heroes in Paris and everyone must prepare a good action for others. Bogged by her activities as Ladybug, Marinette did not have time to prepare hers. For fear of disappointing her friends by announcing that she has not prepared anything, Marinette lies to them and finds herself quickly overcome by her own lie. Her nightmare is just beginning...
Hawk Moth has akumatized his assistant Nathalie into Catalyst, a supervillain that will allow him to put into action the plan he's been concocting for a long time, that will finally make it possible to defeat Ladybug and Cat Noir.