This is not a Discworld book. It is, however, an alternate reality.
In this alternate reality, Russian Influenza has killed the entire Royal family, with the exception of a lone descendant, who has recently become the Governor of a remote island. This descendant has sent for his daughter to join him, on a ship known as the Sweet Judy.
In this alternate reality, there is an even more remote island, known as The Nation. On an even smaller island near the Nation, a boy is building a canoe. He will paddle this canoe back to the Nation, where all the people of the Nation are waiting, and in doing so, he will become a man.
In this alternate reality, there is a tsunami. When it has passed, the boy paddles his canoe to find that the people of the Nation are all dead. The Sweet Judy sits wrecked in the middle of the Nation, the daughter the only survivor.
And from there, the girl and the boy rebuild. That, of course, is only the start.
This is a book full of cliches - the proper English girl, the native boy. The priest, the wise woman. The mothers, one full of light, the other broken, her child her only link to the rest of the world. The brothers, one large and silent, the other small and noisy. The cannibals, the criminals, the sociopath. The widowed father, the bitter grandmother.
Then, with a deft touch, they are more. Ermitrude changes her name to Daphne and approaches life with the mind of a scientist. Mau, who cannot read words, tries to read the universe, the minds of the gods themselves. He fills the empty hole of his Nation with rage and the responsibility of those that are left, those that arrive as refugees. The priest, who demands fealty to the gods, not for the power that is then transferred to him, but because he plagued by questions that are echoes of Mau's. The cannibal king looks a lot like the English Prime Minister. The illiterate natives look upon a cave of wonders and are smart enough to recognise what it means. When faced with the prospect of being dragged into the Empire, they request to be part of the Royal Society instead, because, once upon a time, a king granted the society a mace as alike in bigness to his own.
This is a book about finding yourself when everything else is taken away. It's about science, and religion, because children raised among the greatest scientific minds in the world will still ask if there are ghosts. It's about the perfect world we're promised and the perfect world we imagine. It's about the wonder of discovery, how everything you think you know is not everything you can know, and the stars don't disappear when the sun rises. It's a painfully beautiful love story that contains no more than a kiss on the cheek.
It breaks my heart, every time I read this book. It's a subtle break, the words hitting you so neatly you don't notice the cracks they leave behind, until a simple phrase touches you like a whisper, and your whole heart shatters. I can't do it justice, I really can't. But for those who've never liked Pratchett because of the whimsy and satire of his Discworld series, you won't find it here. There's a few bright feathers of comic relief, and some sly digs, but forget about 'madcap'. That never even entered this book.
It would be impossible to review this book without mentioning the fact that it is the first Pratchett wrote after his diagnosis of early-onset Alzheimer's. There's no denying the analogy between the tsunami that stole a young boy's people, and the writer's disease that steals the Nation of his own mind. I don't doubt that Mau's rage against gods who would do this was echoed by the writer giving him those words.
But I also can't help but wonder if this was also the book that Pratchett always wanted to write, the Masterpiece he thought he'd have more time to write, then, when faced with the reality of time running out, poured out his pain and despair and philosophies and, above all, hope for a better world. No, wait. Not just hope, and not just a better world. His determination for a perfect world.
The creation myth of the Nation states that Imo made the world, then made people from the souls of some dolphins. Then, when there were too many people, he made Locaha, the god of death.
Eventually, Imo realised the world he'd made wasn't so good, so he decided to destroy it and make a perfect world. But Locaha asked instead that this world be given to him. When people died, he would turn them into dolphins, until it was their turn to be born again. But 'when I find a creature who has stiven, who has become more than the mud from which they were made, who has glorified this mean world by being part of it, then I will open a door for them into your perfect world and they will no longer be creatures of time for they will wear stars.'
Later in the book, Locaha speaks again.
Those other I mentioned, who have been shown the glittering path? The all said the same thing as you did. They saw that the perfect world is a journey, not a place. I have only one choice, Mau, but I'm good at making it.