In the year 1800, the dreaded scourge of smallpox spread through villages, towns and cities in swift epidemics. Whole populations ran in panic to escape - but there was no escape! Then, in Cambridge, Massachusetts, which was as yet untouched by smallpox, a doctor named Benjamin Waterhouse addressed the members of the town council, with evidence from England that smallpox could be wiped out in time - by vaccinating everyone with cowpox before the epidemic reaches them...