The chrysalids - John Wyndham

David's father doesn't approve of Angus Morton's unusually large
horses, calling them blasphemies against nature. And blasphemies, as everyone knows, should be burned: KEEP PURE THE STOCK OF THE LORD; WATCH THOU FOR THE MUTANT.

Little does he realise
that his own son - and his son's cousin Rosalind and their friends - have
their own secret aberration which would label them as mutants. And mutants, as everyone knows, should be burned.

But as
David and Rosalind grow older it becomes more difficult to conceal their
differences from the village elders.
Soon they face a choice: wait for
eventual discovery - and death - or flee to the terrifying and mutable Badlands . . .