The Chrysalids - John Wyndham

Genetic mutation has devastated the world. In the bleak, primitive society that has emerged from its ruins, any sign of deviation is ruthlessly hunted out and destroyed. David lives in fear of discovery, for he is part of a secret group of children who are able to communicate with each other by transferring thought-shapes into each others minds. As they grow older they feel increasingly isolated. Then one of them marries a norm with terrifying consequences.