Peter Dickinson

The realm of magic is being threatened by the realm of logic, so the green wizard, Carolinus, decides to shield it for all time. Ommadon, the evil red wizard, stands in his way. Carolinus then calls for a quest that is to be led by a man named Peter Dickinson, who is the first man of both the realms of science and magic. It is Peter's job to defeat Ommadon.

In a post-apocalyptic Britain, everyone has rebelled against modern technology (electricity, engines, trains etc) and reverted to a pre-Industrial Revolution way of life. When Nicky Gore tries to investigate the cause, she is accused of being a witch and imprisoned to prevent her spreading dissent.