Why must we put things in boxes - this is an adult novel, this is for children? Because if no-one over the age of 16 ever reads this then they are missing out.
A short novel, but beautifuly crafted to reveal step by step an agnozingly scarey world so differenet from our own, but so much the same. Some may say drop it into the box marked science fiction, but it is not.
Much of Jan Mark's writing deals with worlds and places which we and the central charater initially accept, but which gradually become darker and more strange as each layer is gadually removed. So here Demetria begins the tale as a child, like any other, on an island that seems initially a bit like something in the Western Isles. Strict, colourless, isolated. Things are the way they are and there is not need to question, or even notice, that anything is "wrong". Until someone from outside comes along.
The second half of the book then becomes almost a mental monologue as everything Demetria knoew, all her certainties, melt away and the final climax is the only possible option.
Another example of why modern "teenage fiction" is the most exciting area of current writing. Not to be missed by anyone of any age.