If the twenty-first century seems an unlikely stage for the return of a 14th-century killer, the authors of Return of the Black Death argue that the plague, which vanquished half of Europe, has only lain dormant, waiting to emerge again-perhaps, in another form. At the heart of their chilling scenario is their contention that the plague was spread by direct human contact (not from rat fleas) and was, in fact, a virus perhaps similar to AIDS and Ebola. Noting the periodic occurrence of plagues throughout history, the authors predict its inevitable re-emergence sometime in the future, transformed by mass mobility and bioterrorism into an even more devastating killer.