The Riddle of the Sands

Carruthers, a minor official in the Foreign Office is contacted by an acquaintance, Davies, asking him to join in a yachting holiday in the Baltic Sea. Carruthers agrees, as his other plans for a holiday have fallen through. He arrives to find that Davies has a small sailing boat, not the comfortable crewed yacht that he expected. Davies gradually reveals that he suspects that the Germans are undertaking something sinister in the German Frisian islands, based on his belief that he was nearly wrecked by a German yacht luring him into a shoal in rough weather. Carruthers and Davies sail back to the Frisian Islands and spend some time exploring the shallow tidal waters of the area, moving closer to the mysterious site where there is a rumoured secret treasure recovery project in progress. They are watched by a German navy patrol boat, which warns them away from the area.

Taking advantage of a thick fog, Davies navigates them covertly through the complicated sandbanks in a small boat to investigate the site. They find that it is actually the centre of a German plan to invade England. The invasion plan is master-minded by a renegade Englishman, but Davies has fallen in love with his daughter and he does not want to hurt her by revealing her father's treason. Eventually they manage to escape with the information and the invasion plan is foiled.