In an unspecified location, an enigmatic and unnamed Asian scientist accidentally smashes a bottle containing a deadly and unnatural virus. The disease quickly spreads across the world through air travel, infecting and killing thousands. In modern-day London, a young woman named Jenny visits her friend Andrew, a physician who is working in a city hospital, to ask him to come see a mutual friend, Pat, who has become ill. The hospital clientele has suffered a high number of deaths from the mysterious disease, but the Home Secretary has instructed the hospital staff to keep it quiet, telling the public it is merely a flu epidemic. Soon, civilisation begins to collapse as the deaths increase, mass absenteeism affects public services, and amenities and the electronic media go off air. Eventually the electricity shuts off, and all public services falter then eventually cease entirely. Jenny and Andrew return to Pat's home to find she has died from the disease, and Andrew reveals the true extent of the situation to Jenny: he too has got the disease, the virus is wiping out thousands, and there is nothing anyone can to do stop or cure it. Andrew orders Jenny, who has displayed an immunity to the virus, to leave London as fast as possible as the countless dead bodies will spread more diseases which she is vulnerable to. Jenny packs her bags and leaves for the country to look for more survivors. Original Broadcast Date 16th April 1975.