Isaac Newton’s most dangerous opponent was not a rival mathematician. He was William Chaloner, born around 1650 to a poor weaver in Warwickshire and apprenticed to a nail maker in Birmingham, a town notorious for forged groats. Chaloner walked to London in the 1680s, found the guilds closed to him, and worked his way up through the underworld: selling tin watches with hidden sex toys, posing as a quack doctor, and playing a psychic who recovered goods he had stolen himself.

This episode follows his climb from street hustles to a counterfeiting operation that bought him a mansion in Knightsbridge, and then to his boldest scheme, persuading the Privy Council that the Royal Mint was corrupt and that he should help run it. He forged Bank of England notes, betrayed his partners to the hangman, and collected rewards for it. Then Newton, as warden of the Mint, built a case too wide for Chaloner to talk his way out of.

• Clipping had stripped English silver coins of nearly half their weight, and smugglers were melting good coins to sell as bullion abroad.
• Chaloner split his operation among a goldsmith, an engraver, his brother in law, and separate distributors, and moved the noisy presses to a house in Egham, Surrey, beyond the reach of London magistrates.
• When the Bank of England issued 100 pound notes on marbled paper in 1695, he got the same paper from its printer. Once caught, he turned informer and received a 200 pound reward.
• Associates Aubrey Price and Matthew Coppinger were both hanged after Chaloner turned them in.
• At the Old Bailey in March 1699 Newton produced eight witnesses, among them wives and widows of men Chaloner had betrayed. He was convicted of high treason and hanged at Tyburn on March 22, 1699.