The Spanish flu was one of the most devastating natural disasters in history, an unstoppable virus that swept the planet in 1918, killing as many as 50 million people. New evidence suggests the possible birthplace was actually in America's heartland. Witness a globe-spanning story of death and denial on an epic scale, as we visit a mass gravesite, pore over old medical records and diaries, and use cutting edge scientific research to reveal the horrific truth behind this deadly pandemic and see if could happen again.