The perplexing story of the flu, a virus that causes fevers and sore throats—and kills more than 30,000 Americans each year. Even now, a century after the great flu pandemic of 1918, which left an estimated 50 to 100 million people dead worldwide, there’s still no cure, writes Brown, an ER veteran and director of the National Institutes of Health’s Office of Emergency Care Research. In his debut, he traces the millions-of-years history of the virus, efforts to understand and treat it, and its many devastating outbreaks. “We know its genetic code, how it mutates, and how it makes us sick, and yet we still don’t have effective ways to fight it,” he writes. The author begins with the 1918 pandemic—“a global health crisis that killed more people than any other illness in recorded history”—which probably began in France, or Kansas, or even China (we do not know), prompted many ineffective treatments (from enemas to bloodletting), and had the worst impact on the elderly and those with compromised immune systems. Found in humans and other species—and able to cross from animals to people, hence the “swine” and “avian” flu—the virus invades cells, reproduces, and moves on to colonize other victims. The 1918 outbreak occurred late in World War I and killed 675,000 Americans, spreading rapidly in crowded tenements, Army camps, and large War Bond rallies. Despite prohibitions, many people kept spitting in the streets. Most cases cured themselves (they still do); others disguised themselves from immune defenses. Antibiotics and preventive vaccines have helped in treatment, but there is no “safe and effective drug that can destroy the virus.” Writing in a conversational style, Brown also covers the discovery of the 1918 virus in frozen victims, the hunt for vaccines, the collection of data, and American efforts to prepare for future outbreaks. One leading expert told him, “I’ve been thinking about the flu for twenty years, and I know nothing.” A solid book of popular science.