Some sort of mystery novel, but what seems to be notable is that it's written as if from the perspective of an autistic person. I first heard about it on my "Helping in Schools" course, where I was very interested to read it until I realised it wasn't written by a person with autism, but about a person with autism, which wasn't how it was sold to me. I heard about it again when reading this article by Meming of Life blogger Dale McGowan, in which it is very highly recommended. Thus I'm curious again, if only for the thought experiment. It got mentioned at university (on my Primary Education course) too, inevitably I suppose.
Bought a second-hand copy for 50p from the Sheffield Buddhist Centre on the 13th of October 2011.
Number 13 on the 2006 World Book Day poll.