This is a fantastic tale of Victorian London, which though at heart is a medical tale, it's ultimately detective work that triumphs over the medical establishment. In the mid-1800s as cholera began to sweep Europe the medical establishment were at a loss, this was before the germ theory of disease and most medical treatment tended still to do more harm. Cholera whilst reasonably lethal to humans can be easily avoided as long as one avoids drinking from a contaminated water supply. Perhaps and observation for us to make today, but in a world before microbes this was still a large leap to make. Hempel skilfully weaves her tale of 19th century London telling us how Jon Snow through is grand experiment managed to unravel the mystery of cholera, along the way were introduced to a whole host of other characters from Florence Nightingale to Queen Victoria and well as presented with many fascinating facts and historical anecdotes. The prose is highly readable having an almost novel like quality to it, the story fascinating and more importantly we witness the legacy that the great cholera outbreaks still have on our society today.