While the United States was embroiled in the Great War overseas, a lethal enemy was at work stateside as well. In October 1918 alone, 195,000 Americans died, making it the deadliest month in American History. The killer was influenza. It infected about 500 million people—one third of the world’s population. At least 50 million people died worldwide, with about 675,000 deaths in the United States. Now, more than a century later, many think influenza is a common and mild disease. Is it? Dr. Jeremy Brown, Director of Emergency Care Research at the National Institutes of Health, gives us an enlightening and unnerving look at the history of this shape-shifting, deadly virus. He believes if we can solve the mysteries of the past, it could protect us from the next outbreak. He also predicts how long it will take before we are able to conquer it for good.