Forty years ago, Steve Smith found a copy of a famous children's book by disgraced author Edith Twyford, its margins full of strange markings and annotations. Wanting to know more, he took it to his English teacher Miss Isles, not realising the chain of events that he was setting in motion. Miss Iles became convinced that the book was the key to solving a puzzle, and that a message in secret code ran through all Twyford's novels. Then Miss Iles disappeared on a class field trip, and Steve's memory won't allow him to remember what happened. Now, out of prison after a long stretch, Steve decides to investigate the mystery that has haunted him for decades. Was Miss Iles murdered? Was she deluded? Or was she right about the code? And is it still in use today?