A teenager with Asperger’s syndrome makes an unlikely but engaging sleuth for David Newnham.

Graham Swift started it. Tell a story - any story - and along the way drop in as many 10-minute talks on tangential topics as you think the reader can take.

In his novel Waterland, we learned about the draining of the Fens, the life cycle of the eel and the growth of the brewing industry in East Anglia during the second half of the 19th century.

It’s a fun and easy way to explore the world. No more ploughing through entire Dick Francis thrillers to learn about horse racing or civil aviation. It is the novel as lucky dip; Tess Of The d’Urbervilles incorporating the Boys’ Book Of Amazing Facts. It is, in short, thoroughly post-modern.

You need a special sort of narrator to make it work, of course - someone who really might fly off at tangents. Swift used a distracted teacher, and Mark Haddon, in a bold move that will guarantee him many hand-wringing column inches in the Sunday papers, uses a teenage boy with Asperger’s syndrome. This was a stroke of genius, as the advantages of having a naive, literal-minded boy in the driving seat are manifold. Particularly when the boy decides to play detective.

Christopher is 15 years, three months and two days old when he stumbles on the body of his next-door neighbour’s poodle impaled on a garden fork.

Against the advice of his father (“Just try and keep your nose out of other people’s businessI”) he decides to cast himself in the role of his hero, Sherlock Holmes, and investigate the “murder” himself.

Blind to the subtler aspects of the standard-issue human mind, he makes an unlikely private eye. Yet he is soon digging up things that were best left buried. But it’s as a narrator that he really excels, as his inability to comprehend metaphor, dishonesty or humour (we frequently find ourselves laughing at jokes that sail above his head) means he can report only what he sees and hears. So it is down to us to work out what is really going on around him.

Not that Haddon ever invites us to laugh at Christopher. Rather, by painting him as incorruptible, he invites first our sympathy, then our admiration. Which is just as well, as the boy has an autistic tendency to share with anyone who will listen such thoughts and associations as enter his head.

And that’s where we find ourselves sampling a range of subjects, from the nature of the Milky Way to the truth about human consciousness, life after death and Sir Arthur Conan Doyle’s embarrassing interest in fairies.

Like Raymond Babbitch(played by Dustin Hoffman) in the 1988 film Rain Man, Christopher is a maths whiz. So not only does he astound us with feats of mental arithmetic, but he also initiates us into the mysteries of prime numbers and introduces us to several classic maths problems, complete with diagrams. No eels this time. But we do learn what it might feel like to have Asperger’s syndrome. And who murdered that wretched poodle, of course.