The Curious Incident of the Dog in the Night-time was a hit novel for Mark Haddon with its analysis of the adventures of a 15 year old boy who has a disorder in the autism spectrum, akin to Asperger's. Haddon says the novel is not a manual on autism but a book about otherness and how society at large reacts to what is different.
What Michael Morpurgo's novel does is to place the horse centre stage, so that episodes in the First World War are seen from an equine point of view. The curious effect is that in this "war to end all wars" you realise that on the opposing side are good men who love horses. You hate what war does because horses get hurt and killed or die of overwork and malnutrition. But how to stage a play where the central character is a horse?