Leana Wen―emergency physician, former Baltimore health commissioner, CNN medical analyst, and Washington Post contributing columnist―has lived on the front lines of public health, leading the fight against the opioid epidemic, outbreaks of infectious disease, maternal and infant mortality, and COVID-19 disinformation. Here, in gripping detail, Wen lays bare the lifesaving work of public health and its innovative approach to social ills, treating gun violence as a contagious disease, for example, and racism as a threat to health.