At the death of Heracles, his friend Philoctetes was the only one to come forward to light the funeral pyre. In return Philoctetes was given Heracles magical bow and arrows. In the middle of the Trojan wars which went on for decades, Philoctetes was bitten by a snake and his leg turned rancid. The smell was so dreadful and noxious to the other sailors and soldiers that Odysseus abandoned Philoctetes on the island of Lemnos and set sail without him. Ten years later Odysseus returns and this is where Kae Tempest's play begins.
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?