An author named Sir Arthur Conan Doyle wrote many stories about the greatest detective in the world and the mysteries he solved. The detective character is called Sherlock Holmes. Maybe you’ve heard of him? But what you may not know is that the author wrote a secret mystery story and hid it somewhere in London. He left behind a series of puzzles and a curious purple cipher ring, only the best detectives will be able to follow them. Rita and Desmond need your help to solve the mystery and find the secret book.