It's summer in London, and things are quiet. But while Holmes and Watson chafe at their inactivity, a train, carrying a vital encoded communication, is entering a tunnel in an obscure region of the Balkans – never to be seen again. The case of the disappearing train is only the beginning of the nation's difficulties. The missing message must be found and decoded, and a diplomat's wife must be rescued from the clutches of a pernicious blackmailer. The nation is in danger, and if a diplomatic scandal of disastrous proportions is to be avoided, Sherlock Holmes' brilliance may not be enough…