The Riddle of the Sands

Set during a sailing trip in the Baltic Sea, this classic spy thriller follows two young adventurers-turned-spies as they uncover a German plot to invade England. Written in 1902 by Royal Navy officer Erskine Childers, it is celebrated as the first modern spy novel, praised for its authentic nautical details, suspenseful spycraft, and influence on later espionage literature.