In 1928, Alexander Fleming noticed something a less-curious scientist would have thrown in the bin — a contaminated petri dish with a mysterious clear halo around a spot of mold. What followed wasn't a eureka moment but a decade of neglect, a world war, and a scramble by two other scientists to turn a curiosity into the drug that would save an estimated 200 million lives. The discovery of penicillin is the story of how accident, abandonment, and desperation accidentally conspired to change what it means to be mortal.