Newton and the Counterfeiter: The Unknown Detective Career of the World's Greatest Scientist by Thomas Levenson is one of those excellent books that evokes the era it describes. It's also one of those books that had me saying "I didn't know that!" about every other page, which is always a treat.
The title and subject sound like they ought to be fiction: After writing his Principia, Newton is appointed Master of the Mint in the middle of a financial crisis. He not only redesigns the process of coining to make it more efficient, he spends his time tracking down counterfeiters. Chaloner, in particular, proved particularly evasive and took Newton's full attention as a detective. It is not fiction: Newton really did have a second career as Master of the Mint and detective, and he was good at it.
Both Newton and Chaloner emerge as strong personalities, foils to one another (though Chaloner never quite seems Newton's equal), and worth the historian's and the casual reader's attention. I shall be looking for Levenson's other work.