Alex Bellos, author of Snowflake Seashell Star, takes the reader on a tour of his favourite mathematical concepts to reveal the hidden numbers that underpin our everyday lives. In the course of his travels he explores the Ordnance Survey's obsession with trigonometry, explains why rollercoasters are a monument to Newton's innovations, ponders why we have superstitions about certain numbers, delves into the mysteries of hyperboloids and meets an anonymous member of a secret mathematical sect.