First, a horse in Brisbane falls ill: fever, swelling, bloody froth. Then thirteen others drop dead. The foreman at the stables becomes ill and the trainer dies. What is going on? As globalization spreads and as we destroy the ancient ecosystems, we encounter strange and dangerous infections that originate in animals but that can be transmitted to humans. Diseases that were contained are being set free and the results are potentially catastrophic. In a journey that takes him from southern China to the Congo, from Bangladesh to Australia, David Quammen tracks these infections to their source and asks what we can do to prevent some new pandemic spreading across the face of the earth.