The first time Marinette's world turned upside down, she had gotten home from school to find a strange box on her desk. When she opened it, Tikki her kwami, introduced herself and told Marinette that if she put on her new Miraculous earrings she could be one a superhero that could save Ivan.
Of course Marinette agreed. She became the superheroine Ladybug and met her partner Chat Noir. Together, they captured Ivan's akuma. That was could be the first of their many missions together.
The second time Marinette's world turned upside down was the day Chat Noir stopped in the middle of patrol. He told her that he couldn't go on without telling her his identity. "Ladybug... This means the world to me..." he said. "Claws in. " There was a flash of green light. In Chat's place, Adrien Agreste stood.
Marinette burst into tears. "You stupid cat! Spots off!" Ladybug's mask melted off her face revealing herself. That night ended with a lot of happy crying, each of them so, so, relieved they were who they were.
The third time her world was knocked upside down, Marinette and Adrien had discovered who Hawkmoth was. Marinette had given Alya, Nino, and Chloe their Miraculous two weeks prior. All five of them had shown up at the Agreste mansion. Ladybug and Chat had located Hawkmoth to the back of Adrien's home. They knew Gabriel had to be the supervision then.
The right was easy enough. Rena Rouge had grabbed the Peacock Miraculous on the way in, so calling in Mayura was impossible. Ladybug had taken Hawkmoth by suprise. She had walked in, snatched the Butterfly Mirqculous, and arrested him.
That night was the hardest. Adrien was now basically an orphan. Marinette took him in for a few months until Nathalie was cleared to be able to raise him. Somehow, though, Marinette knew her world was going to turn upside down again soon.