In the space of about two years, between the spring of 1918 and the spring of 1920, a single strain of influenza circled the entire inhabited world. It infected perhaps five hundred million people ? one in every three human beings then alive ? and it killed somewhere between twenty-five and fifty million of them, possibly far more. More died than in all four years of the First World War that framed it. And then, almost unbelievably, the world chose very nearly to forget.

This is the whole sweep of the catastrophe in a single volume: the obscure beginnings on the American prairie and in the great army camps; the mild first wave and the deceptive summer calm; the lethal second wave that turned strong young men blue and drowned them in their own lungs in a matter of hours; the closing of the cities, the mask wars, the parade in Philadelphia and the early action in St. Louis that meant the difference between catastrophe and survival. It follows the virus far beyond the West ? to India, where it killed more than anywhere on earth; to Persia and Africa and the Pacific, where whole communities were swept away; and to the two Samoas, where a single decision about quarantine meant a quarter of one population dead and not a soul lost in the other.

Vivid, sourced, and clear-eyed, this is a popular history that gives the dying its due without sensationalism, that explains the science clearly ? why the young died, why the name 'Spanish' was a slander, how the virus was finally recovered from the Arctic permafrost and brought back to life in 2005 ? and that confronts the great mystery of the forgetting. It is the story of the year the world fell ill, told in the conviction that a catastrophe forgotten is a catastrophe half-prepared to happen again.