Marinette had always been able to seamlessly separate her super hero life from her civilian childhood. But when random items in Adrien's bedroom begin to disappear and leave ransom notes from Hawkmoth in their places, she worries that the villain is somehow hurting her crush to intimidate Ladybug.
She rushes off to Chat Noir for help, and admits that "that random boy" 's troubles are her fault. What he doesn't tell her is that he is Adrien Agreste, and that the threats are aimed towards Chat Noir. After all, he wasn't about tell the beautiful ladybug that he caused her stresses.
This inevitably leads to drama, love, danger, and the dreaded love square we've all come to appreciate (from a far).