Medicine, in the early 1800s, was a brutal business. Operations were performed without anaesthesia while conventional treatment relied on leeches, cupping and toxic potions. The most surgeons could offer by way of pain relief was a large swig of brandy. Onto this scene came John Elliotson, the dazzling new hope of the medical world. Charismatic and ambitious, Elliotson was determined to transform medicine from a hodge-podge of archaic remedies into a practice informed by the latest science. In this aim he was backed by Thomas Wakley, founder of the new magazine, the Lancet, 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. The mesmerism mania would take the nation by storm but would ultimately split the two friends, and the medical world, asunder - throwing into focus fundamental questions about the fine line between medicine and quackery, between science and superstition.