It starts quietly enough. It will pass, you think. But it doesn't. In fact, it emerges all around the globe, evolving into a plague - and killing people only days later. Teacher Kit Chaplin is struggling to understand what he is witnessing. Even Lilly Slater, his partner and an eminent vaccinologist, can't understand it. As it spreads, they are inexorably drawn into the mystery behind the illness. This piercingly insightful novel tells the story of a global catastrophe through the eyes of the three people at the heart of the storm.