'This telegram is from my brother Mycroft,' said Holmes. 'He wants to speak to me at once about Mr Arthur Cadogan. Do you know this man, Watson?' 'I saw something about him in today's newspaper,' I answered. When a young man dies on a London Underground line, top-secret plans for a new British submarine go missing. But who is Cadogan's killer, why did he die, and where are the missing papers? Sherlock Holmes and Doctor Watson must quickly help Mycroft to answer these important questions.