Medicine in the early 1800s was a brutal business. Operations were performed without anaesthesia while conventional treatment relied on leeches, cupping and toxic potions. It was said of one surgeon, 'His surgical acquirements were very small, his operations generally very badly performed and accompanied with much bungling, if not worse.' It was lucky, for the doctor at least, that his deafness made him immune to his patients' dying groans.

Into this milieu came John Elliotson, the dazzling new hope of the medical world. Charismatic and ambitious, Elliotson was determined to transform medicine from a medieval hodgepodge of archaic remedies into a practice informed by the latest science. In this aim he was backed by Thomas Wakley, founder of the new Lancet magazine and a campaigner against corruption and malpractice. Then, in the summer of 1837, a French visitor - the self-styled Baron Jules Denis Dupotet - arrived in London to promote an exotic new idea: mesmerism. It was a trend that would take the nation by storm but would ultimately split the two friends, and the medical world, asunder, throwing into sharp focus fundamental questions about the line between medicine and quackery, between science and superstition.