Isaac Newton’s fame is such that it would seem that almost nothing remains to be discovered about his career or methods. But very little attention has been paid to the three decades Newton spent in charge of the Royal Mint, and especially to the first of those years, in which he supervised the remaking of England’s entire silver money supply, all the while investigating and prosecuting the nation’s currency criminals. Records of Newton’s criminal investigations survive, providing a unique window on both his own habits of mind, his approach to problems, and on how what has come to be called the scientific revolution played out, not just in the minds of the great, but on the streets of seventeenth century London.