The Riddle of the Sands, a work of espionage and military strategy, centers on Davies and Carruthers, a minor official in the Foreign Office, and their suspicion of a German plot to invade England. Navigating a tiny sail boat up a sandbank-ridden waterway, Davies and Carruthers explore the shallow tide beaches and stumble upon a mysterious site rumored to be the place of hidden treasure. Refusing to heed the warnings of a German navy patrol boat, Davies and Carruthers continue on, but the plot thickens as Davies falls in love with the daughter of the supposed mastermind behind the invasion plot.