The first half of the novel unfolds a mystery as an Englishman by the name of Edward Prendick is shipwrecked and rescued by another ship en route to the titular island. Slowly Prendick discovers what is happening: a mad god by the name of Dr. Moreau is creating for himself a race of men from the dust of vivisected animals. His act of creation is one of unmitigated cruelty and suffering, the laboratory religiously feared as the House of Pain. This mad god is fashioning creatures from the wild stuff of nature and then expects them to act contrary to their natures, forcing upon them a law that further adds to their discomfort. Carnivorous animals are prohibited from eating meat and lapping water on all fours is verbotten. I can't help but wonder if Wells' notorious philandering had anything to do with this metaphor.
Eventually the beast-men rise up and destroy their god, and here is where the story actually starts to get philosophically interesting. It is one thing to say that God is a meanie poo-face and religion uses fear to stop you from having fun. That part is easy. Wells takes this fairly typical objection and turns it on his ear when Prendick is left alone on the island with the beast-men. Without the authority of Dr. Moreau to strike terror into the conscience of his creations, the beast-men are quickly reverting back to their animalistic selves. Life is going back to a state of nature in all its nastiness, brutishness and brevity. Prendick's sole recourse is to become a religious prophet. To justify the law, he preaches that some day Dr. Moreau will return with the House of Pain to punish all those who have sinned. Once again the symbolism is transparent but the implications are provocative: religion may be a lie, but it is a necessary one.
In the end our protagonist is rescued, but is struck with the existential dread that Wells no doubt hoped to inflict on his readers:
I could not persuade myself that the men and women I met were not also another Beast People, animals half wrought into the outward image of human souls, and that they would presently begin to revert,—to show first this bestial mark and then that... I see faces, keen and bright; others dull or dangerous; others, unsteady, insincere,—none that have the calm authority of a reasonable soul. I feel as though the animal was surging up through them; that presently the degradation of the Islanders will be played over again on a larger scale...
Then I would turn aside into some chapel,—and even there, such was my disturbance, it seemed that the preacher gibbered "Big Thinks," even as the Ape-man had done...
Damnit Herbert! The Island of Doctor Moreau is a textbook example of how H.G. Wells' early work falls into that most diabolically crude class of English allegory, the type in which the Lion is Jesus and the Martians are us. Oh, I get it, symbolism. G.K. Chesterton, who being an Englishman was not immune to this cultural trait, once said of his nemesis: "Mr. Wells is a born storyteller who has sold his birthright for a pot of message."