As the inventor of the separate-condenser steam engine – that Promethean symbol of technological innovation and industrial progress – James Watt has become synonymous with the spirit of invention, while his last name has long been immortalized as the very measurement of power. But contrary to popular belief, Watt did not single-handedly bring about the steam revolution. His perfect engine was as much a product of late-nineteenth-century Britain as it was of the inventor’s imagination. As one of the greatest technological developments in human history, the steam engine was a major progenitor of the Industrial Revolution, but it was also symptomatic of its many problems. Armed with a patent on the separate-condenser principle and many influential political connections, Watt and his business partner Matthew Boulton fought to maintain a twenty-five-year monopoly on steam power that stifled innovation and ruthlessly crushed competition. After tinkering with boiling kettles and struggling with leaky cylinders for years without success, Watt would eventually amass a fortune and hold sway over an industry. But, as Ben Marsden shows, he owed his astonishing rise as much to espionage and political maneuvering as to his own creativity and determination. This is a tale of science and technology in tandem, of factory show-spaces and international espionage, of bankruptcy and brain drains, lobbying and legislation, and patents and pirates. It reveals how James Watt – warts and all – became an icon fit for an age of industry and invention.