Much as in Arthur C. Clarke's Childhood's End (and in John Wyndham's own The Midwich Cuckoos), The Chrysalids posits a future transformed by children putting their minds together in ways adults can't.
Following a Tribulation (given the evidence, a nuclear war) that took place possibly thousands of years in the past, life has become simpler and narrower, at least for people living in Labrador. There's government and civil society, and a steam engine appears to be this culture's technological leap. People are aware that there was a former world of great marvels, but these Old People brought ruin upon themselves; the predominant view seems to be that the destruction wrought was ordained by God, and given that the most notable surviving texts from the former time are the Bible and some much later religious text, what has emerged in a culture like that of the Puritans, focused on family, fearful of what might be in violation of the Creator's will.
"The mutant" is the greatest evil: any deviant plant or other lifeform should be destroyed. As even one of the heterodox characters points out, such a position is reasonable given that, in the wilder regions south of our setting, nature has sprouted forms at odds with existing species, and, if you're going to be cultivating plants and practicing animal husbandry, you ought to exercise control over biological developments. But is every new form evil? A breed of giant horses is accepted by the government, and the local leader—and father or David, our protagonist—thinks this represents a moral failing by pragmatic politicians.
The real problem is for humans who don't follow "the true form," a form preached about and sung about, the human form that the Old People and the people of the Bible possessed (though, as is pointed out, the Bible is unclear about how exactly its humans look). David's first best friend, Sophie, has an extra toe, leading to his first rift with his father and his people. But that's just a hint of the larger rift to come, as David, and others, discover telepathic abilities. To say more is to give away too much of the plot, but Wyndham manages to set in motion a host of plot threads that all converge pretty well at the end. It's a satisfying story.
How Wyndham tells the story, however, is a mixed bag. There's nothing special about the voice: it's pretty standard, calm, clear storytelling in the English style, with some dramatic beats tossed in. It reads smoothly. Much of the story is conveyed through summary, as David describes the passage of years or the long development of a relationship. The most important relationship in the novel, David's with his lover, takes place almost entirely in passing, vague references, then in summary, until we finally see the two of them together, which doesn't help us see the relationship in the profound terms David does. There are several good scenes in the novel (though one takes place for which David clearly isn't present), but much more exposition and—because of the central premise of telepathy—dialogue between and among people who can't see each other. Even when people are together, they tend toward lengthy pronouncements and explanations, again undercutting the drama.
A few times, Wyndham seems aware of this problem, as David, stuck "listening" to someone's "thought-shapes," tunes the person out or comments on their problematic tone (since people projecting their thoughts can't read the doubtful reactions of their listeners). Even so, the dialogue is interesting, not as stiff as such a structure might lead you to expect.
An enjoyable book all around. It has elements of the other two Wyndham books I've read (Day of the Triffids contains things that don't grow as they ought), but the story is better. Triffids felt aimless and odd; The Midwich Cuckoos had a narrator watching things at arms-length. David isn't a memorable character, but he has relatable conflicts such as how to take what adults are telling him, and whether to conceal things from his parents. The book also takes a strange philosophical path at the end which may not actually be the writer's point of view, and David questions whether he's going from one autocratic perspective to another, though, by the final scene, he seems to have dropped that question.