On August 21, 1986, the farmers around Lake Nyos in Cameroon went to sleep in a silent valley. By morning, every living thing-1,746 people, 3,500 livestock, even the flies-was dead. There was no fire, no flood, and no violence. The killer was the lake itself. This book investigates the terrifying phenomenon of a limnic eruption, where a lake "burps" a massive cloud of carbon dioxide, displacing oxygen and drowning a valley in invisible gas. It follows the scientific detective story to understand the event, the race to degas the lake before it strikes again, and the geological ticking time bombs hiding in crater lakes around the world. A gripping look at how the earth breathes, and sometimes, holds its breath too long.