Milton doesn't know much about Castle Cryptic, but finds himself drawn there all the same. He thinks it's a summer camp for gifted children. Instead, it's a world of spells and riddles, run by magicians who work to protect us all. Their allies include Sir Marmaduke Wax - who runs a secret library in Oxford - and the Knights of the Moonlit Chamber, who beam themselves through space and time using the radio telescopes at Jodrell Bank. Becoming a junior researcher there, Milton spends much of his time in a dark projector room, viewing strange scenes from nowhere on Earth. At the same time, his friend Margaret learns how to talk to trees - and the trees talk back. They inform her of a heinous plot in another world, with dire consequences for our own. In the wake of this revelation, Milton and his new friends go up against sorcerers and saboteurs, hoping to avert disaster before it's too late...