She was called angry, irascible, and combative. But more than anything else? She was correct. Ask most people what they know about DNA and they might be able to tell you some basics: It exists inside every living thing. It holds the genetic code that controls much of our development and behavior. And it’s shaped like a double helix—a structure that holds the key to understanding how it works. But who first figured out the structure of DNA? Who unlocked this crucial key? That’s where Rosalind Franklin came in. Even as a child, Franklin was passionate about science, and that passion drove her to become a chemist and X-ray crystallographer. Over the course of her career, she studied elements, viruses, and DNA, capturing the first clear image of DNA’s helical structure. But as one of the few women working in science during the 1940s, Franklin faced barriers every step of the way. She believed in finding all the facts and refusing to take shortcuts, while others tried to leapfrog ahead of her with sloppy guesswork. When she disagreed with or stood up to men she worked with, she was labeled difficult, angry, and combative. Her male colleagues dismissed her—and eventually stole her work, winning a Nobel Prize for a discovery they didn’t make. This is the story of Rosalind Franklin’s courageous and complex life, her game-changing contributions to science, and the double helix at the center of it all.