Isaac Newton was a complex man. Every student learns of (but few master) the laws bearing his name that govern the motion of objects from bullets to planets. Many know that the same great mind invented calculus along the way toward his Principia Mathematica. But Newton was also intrigued with alchemy throughout his life, and filled notebook after notebook with descriptions of experimental results. He may even have had a mental breakdown as a consequence of depression after a promising route to transmutation collapsed. Newton never married, and little is known of any life we would call "personal", but Thomas Levenson has unearthed a rich trove of original material related to Newton's job in later life, Warden of the Mint. At the time (1687-1702), England was fighting a war with France while her currency was both being counterfeited and undermined by silver/gold arbitrage. The greatest physicist turned into a relentless and ferocious defender of the coin of the realm. He used intense coercion to induce counterfeiters to turn on one another and often obtained the death penalty for those convicted. Levenson focuses on a particular notorious culprit, William Chaloner, but it was clear that Newton was fighting a host of clever counterfeiters, and that he waged an effective, ferocious defense of England's money.