This is a completely brilliant book. The illustrations are fantastic and the research that backs up the content is exemplary. The book starts with the tragic and true story of Ada, Countess of Lovelace and her involvement with Charles Babbage, a 19th century inventor obsessed with the idea of using machines to perform mathematical calculations.
Ada has a background story that you really couldn't make up and the tale of how a poet's daughter became the first person on the planet to really think about what a computer could do is a compelling one.
Once the facts have been dealt with the action moves on into a parallel "Pocket Universe" where Lovelace and Babbage have built their huge steam-powered "Difference Engine" and are using it to solve mysteries and fight crime.
The narrative is littered with historical quotes and insights into maths and computing theory and gives a great introduction to what computers are about and where they came from. At the back you find get a series of appendices that supply plenty of historical context and by the end you really feel for the characters, in both their real and imagined forms.
Everyone should buy this book. It's just wonderful.