When is a new global epidemic going to strike? This in-depth investigation examines the invisible threat of new viruses emerging in the animal kingdom at an unprecedented rate. In the space of 60 years, over 350 new infectious diseases have appeared, including SARS, H1N1, H5N1 and Ebola. This film traces three threatening viruses that have been transmitted from animals to humans: the H7N9 flu virus in Asia; the Mers-CoV virus, related to SARS, active in the Middle East; and the Ebola virus, which is striking terror in West Africa. Researchers are recognizing that a "one health" approach, in which we look at habitat loss and ecosystem breakdown as well as human health, will be crucial for prevention.