Mexican American Mario Molina was a modern-day hero who helped solve the ozone crisis of the 1980s. Growing up in Mexico City, Mario was a curious boy who studied hidden worlds through a microscope. As a young man in California, he discovered that CFCs, used in millions of refrigerators and spray cans, were tearing a hole in Earth's protective ozone layer. Mario knew the world had to be warned--and quickly. Mario went on to become a Nobel laureate and a recipient of the Presidential Medal of Freedom. His inspiring story gives hope in fighting the ongoing climate crisis.