This program helps viewers learn the basics about diseases, the immune system, evolution, and genetics. The program begins with a brief history of the discovery of viruses from Van Leewenhoek to today. Animation shows how viruses are structured, how they replicate, and how they kill healthy cells. Viewers are taken on a tour of the human body as they discover the role played by viruses in chronic diseases like multiple sclerosis, polio, herpes, and HIV. Viruses such as Ebola and Hanta are also discussed.