Title: The Curious Incident of the Dog in the Night-Time.
Author: Mark Haddon.
Description: A mathematically gifted kid tries to solve the mystery of a dog murdered in the night-time.
Remark: Although this isn't a math book per se, it actually does contain a lot of interesting and non-trivial mathematics. Also, it's very well illustrated. As a final selling point, you have to respect any book whose chapters are indexed by the primes.