What I wanted to say was how much I agree with you about John Christopher and I wish that more of his work was still in print. Did you read a trilogy that i think began with a book called ‘New World’ that explored the notion of parallel worlds before ever either Diana Wynne Jones or Philip Pullman did? I can’t find any of those now, not even in the library system. My favourite, however, was a stand alone book, called ‘The Guardians’. It covered some of the same notions that John Wyndham had written about, but for a slightly younger audience. Again, I think it must now be out of print. It’s a real shame. There are far too few writers of good sci-fi for children.