First, a horse in Brisbane falls ill: fever, swelling, bloody froth. Then thirteen others perish. The foreman at the stables becomes ill and the trainer dies.

What is going on? It takes months to establish that the cause is a virus which has travelled from a tree-dwelling bat to horse, and from horse to man. The bats had lived undisturbed for centuries in Queensland's eucalyptus forests. Now the forests are being cut down and the colonies of bats are roosting elsewhere..."Spillover" tells the story of such diseases.

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 Cameroon to Kinshasa, 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.