If you are interested in finding a book to read with the goal of learning more about Isaac Newton... read another book. If, on the other hand, you are interested in a reasonably entertaining historical murder mystery - check this out.
The Newton we meet here is more Sherlock Holmes than, well, Newton. The story is told by his clerk, who happens to be a swashbuckling, pistol-toting rakehell. (Newton was aware that there were plots afoot, and that he might need some protection, you see.)
It's set at the time when Newton was in charge of England's Mint, in the Tower of London, which involved finding and prosecuting forgers. In the course of Newton and his clerk pursuing these duties, a whole bunch of murders happen, there are encoded messages, a possible Templar treasure connection, conflicts between Catholics and Protestants, issues with anti-British French Huguenots, opium-addled prostitutes, sword duels and alchemy.
The plot moves along without getting boring, and I thought that Kerr did a good job of making the language feel period-appropriate without it feeling stilted or awkward to read.
After all the action, it ends on a surprisingly (and slightly jarring) philosophical and downbeat note, but I didn't really mind that. But, as I said - you're not really going to learn a lot about Newton that you didn't already know.