The movie begins with Ladybug and Cat Noir joining a school field trip to New York City. When they arrive, they are surprised to find out that American superheroes exist and that they are just as popular as they are in Paris.
During their first day in the city, Ladybug and Cat Noir meet the American superheroes, who are called the "United HeroeZ." The team is made up of several heroes, each with their own unique powers and abilities. As they get to know each other, they learn that they have a lot in common, including the fact that they all use their powers to protect the city and its citizens.
However, their newfound friendship is quickly put to the test when an akumatised super-villain starts wreaking havoc in the city. The villain has the ability to control machines and uses this power to take control of the city's infrastructure, causing chaos and destruction wherever they go.
Ladybug and Cat Noir join forces with the United HeroeZ to try and stop the villain and save the city. As they work together, they discover that the villain has been akumatised by someone they all know and must find a way to stop them before it's too late.
Throughout the movie, Ladybug and Cat Noir continue to learn more about the United HeroeZ and the world of superheroes in America. They are also introduced to new villains and allies, making this an exciting new adventure in the Miraculous universe.
In the end, Ladybug and Cat Noir successfully save the city and help the United HeroeZ defeat the villain. They say their goodbyes to their new friends and continue on with their journey, ready for whatever challenges come their way.