Riddle of the Sands (a Record of Secret Service) : (Introductory Notes from MI5 and the National Archive)2013

The Riddle of the Sands is set during the long suspicious years leading up to the First World War. Bored with his life in London, a young man accepts an invitation to join a friend on a sailing holiday in the Baltic. A vivid exploration of the mysteries of seamanship, the story builds in excitement as together the two adventurers discover a German plot to invade England.