Carruthers is rescued from a hot summer at a deserted Foreign Office in London, by an out-of-the-blue invitation to join an acquaintance, Davis, on his yacht in the Baltic. He arrives to find not only that he comprises the whole crew, but also that Davies needs his help in a spying mission with enormous stakes. The Riddle of the Sands, with its early warnings of the dangers of a German invasion by sea, created a sensation when it appeared in 1903. It is the forerunner of the spy novels of John Le Carré and Graham Greene, and its detail and dry humour have made it a classic for sailors as well as for thriller addicts.