They weren't God's last word, like they thought: God doesn't have any last word. If He did He'd be dead. But He isn't dead; and He changes and grows, just like everything else that's alive. So when they were doing their best to get everything fixed and tidy on some kind of eternal lines they'd thought up for themselves, He sent along Tribulation to bust it up and remind 'em that life is change. (p. 496, The John Wyndham Omnibus.)
It's many years -- a thousand? more? less? -- after the Tribulation, God's punishment for humanity's hubris. David is a young boy growing up in the rural community of Waknuk. To the south and southwest are the Badlands, where nothing can live; between Waknuk and the Badlands lie the Fringes, where Blasphemies -- those who are not quite human, as evinced by irregular numbers of fingers and toes, or other, less obvious wrongnesses -- are exiled.
David first begins to question the status quo when his childhood friend Sophie is captured and exiled. (It was only a little toe.) Then his Uncle Axel warns him never, ever to mention to anyone that he can speak to some of his friends, no matter how far away they are. But David's little sister Petra is a stronger mind-speaker than any of the others, and it's going to be hard to conceal her gifts ...
Published in 1955 -- ten years after Hiroshima -- this must have been one of the earliest SF novels to explore the world after a nuclear holocaust. It felt dated to me, because so many of the ideas Wyndham includes (mutations of the mind, feral tribes of exiles, technological regression) have become staples of the genre.
The Chrysalids is a powerful novel about evolution and mutation, about purity versus diversity. There are undertones of racism and sexism -- probably more uncomfortable to a modern reader than to the original audience. The moral issues raised (including the draconian measures of the Sealanders) are still unsettling, and Wyndham's hope that greater understanding and communication would bring about peace on earth seems quaint and optimistic.
Incidentally, one passage in this novel sprang out at me. "The way wound somewhat with the lie of the land, but its general direction was right. We followed it for fully ten miles ..." (p.485 of Wyndham Omnibus). I remember that passage from a single June morning in 1983: it was the 'continue this story' part of my English Language 'O' level paper. I'm pretty sure I haven't encountered it between then and now, but ... it leapt off the page, all familiar and known. Memory is a strange thing!