The Ghost Map" by Steven Johnson. It tells the story of how two individuals, Dr. John Snow, who created a map of the cholera cases, and the Reverend Henry Whitehead, whose extensive knowledge of the local community helped solve the mystery of perhaps the most intense outbreak of cholera in Victorian London (See 1854 Broad Street cholera outbreak). At the time the majority of London's intellectual elite embraced the miasma theory (e.g., Charles Dickens, Florence Nightingale), which held that diseases such as cholera or the Black Death were caused by pollution or "bad air."
Snow was skeptical, however, believing that cholera spreads through water contaminated by human waste, and along with Whitehead, whose possessed immense knowledge of the local community through of his frequent visits with his parishioners (especially during the outbreak), they eventually convinced the authorities that the source of the disease was the public water pump on Broad Street (now Broadwick Street). Convincing the authorities was no easy task, however. The idea that diseases could be spread by germs was greeted by many of those to whom Snow and Whitehead appealed (e.g. the press, leading scientists) with scorn. In the end, though, they won the day.
Interestingly, Whitehead was initially skeptical of Snow's theory. Like most intellectuals of his day, he adhered to the miasma theory. However, Snow's research, in particular his (ghost) maps of the Soho area cholera victims, eventually convinced Whitehead that the Broad Street pump was the source of the disease. Moreover, the combination of Whitehead's field work and Snow's demographic analysis set an important methodological precedent in the relatively new field of epidemiology.