On the second floor of the General Society of Mechanics and Tradesmen building in New York City rests an extraordinary display of craftsmanship and ingenuity from the nineteenth century: the John Mossman Collection of bank vault locks and time locks, designed to protect America's riches from every threat. From these beautiful devices we can see the evolution of lock technology during its most creative period. Many of the hand-crafted masterpieces are decorated with beautiful engraving and casting, despite the fact that their mechanical interiors would rarely be seen. They reflect the great pride in creative workmanship and the mechanical genius that characterised American inventions of the time. Two experts on the subject, John and David Erroll, provide the fascinating history of these marvels of complexity, and noted photographer Anne Day provides stunning photographs, combining to illuminate a remarkable but little-known chapter in American technological achievement.