Originally published: New York: Pantheon, 2015.

When Ada translated her friend Babbage's plans for the 'Difference Engine,' her lengthy footnotes contained the first appearance of the general computing theory - 100 years before an actual computer was built. Sadly, Lovelace died of cancer a few years after publishing the paper, and Babbage never built any of his machines. But now Sydney Padua gives us an alternate reality in which Lovelace and Babbage do build the 'Difference Engine', and then use it to do battle with the American banking system, the publishing industry, their own fears that their project will lose funding, and a villainous street musician who will force the two friends to re-evaluate their priorities - 'for the sake of both London and science.'