David, the young hero of the novel, lives in a tight-knit community of religious and genetic fundamentalists, who exist in a state of constant alert for any deviation from what they perceive as the norm of God's creation, deviations broadly classified as "offenses" and "blasphemies." Offenses consist of plants and animals that are in any way unusual, and these are publicly burned to the accompaniment of the singing of hymns. Blasphemies are human beings - ones who show any sign of abnormality, however trivial. They are banished from human society, cast out to live in the wild country where, as the authorities say, nothing is reliable and the devil does his work. David grows up surrounded by admonitions: KEEP PURE THE STOCK OF THE LORD; WATCH THOU FOR THE MUTANT.
At first he hardly questions them, though he is shocked when his sternly pious father and rigidly compliant mother force his aunt to forsake her baby. It is a while before he realizes that he too is out of the ordinary, in possession of a power that could doom him to death or introduce him to a new, hitherto-unimagined world of freedom.
The Chrysalids is a perfectly conceived and constructed work from the classic era of science fiction. It is a Voltairean philosophical tale that has as much resonance in our own day, when genetic and religious fundamentalism are both on the march, as when it was written during the Cold War.