In twelve dreams, Robert, a boy who hates math, meets a Number Devil, who leads him to discover the amazing world of numbers: infinite numbers, prime numbers, Fibonacci numbers, numbers that magically appear in triangles, and numbers that expand without end. As we dream with him, we are taken further and further into mathematical theory, where ideas eventually take flight, until everyone―from those who fumble over fractions to those who solve complex equations in their heads―winds up marveling at what numbers can do.