In this remarkable account, evolutionary biologist Christopher Wills takes us on a voyage of discovery through the exotic pasts of the viruses and bacteria that periodically emerge with such disastrous results for our species. It is our knowledge of their secret lives, the eons spent quietly passing in and out of myriad other life forms, mutating and coadapting, that gives us hope of taming them. By putting these organisms—from bubonic plague to Ebola—at center-stage, Wills shows how we will eventually master them.