The Wikipedia article on it is fairly good. Essentially it's a post nuclear war world in which the human village in the story casts out anyone who is not 'perfect' (ie. mutants) but several of the children have developed the non-obvious mutation of telepathy, to greater or lesser degrees.Not familiar with it. Links to a wiki or quick run down if the basic idea are fine. It's why I'm asking for advice.
I know a thing or two about NZ. It's some pointless country somewhere iirc. Movie land right?
Wyndham also wrote "Day of the Triffids", which has had several movie adaptations.