There is a strange and deadly new virus in Asia, and it claims the lives of nearly 50% of its victims. A team of virus hunters travels to Bangladesh, the latest front in the battle against the recently-discovered Nipah virus, to capture the puppy-sized bats that are believed to be the source of this frightening killer. We'll also trace the evolution of AIDS, SARS, West Nile, the Spanish Flu and the Avian Flu - all diseases that made the jump from animal to human, and then human to human. Increasingly, our global progress is itself a factor that helps these viruses to become resilient. What seems exotic and distant in Africa or Asia today could arrive on our doorsteps tomorrow. Is Nipah the next epidemic?