 Central to the plot is the case of Janet Parker, the last person known to have died of smallpox, which she contracted in 1978 due to a lab accident in Birmingham, England, after the disease was eradicated in the wild.Cornwell makes the villain a junior employee of the lab at the time who was made a scapegoat for the accident and whose career was blighted as a result.This provides the plot with a credible source for the virus and a motive for the central crime.