A ripping good international spy adventure from 1903

The Riddle of the Sands: A Record of the Secret Service Recently Achieved by Erskine Childers is a classic. Ken Follett, the author of The Eye of the Needle and other thrillers and historical fiction, calls it "The first modern thriller." 

First published in 1903, the novel is in some ways a boy's adventure story as two friends from Cambridge work to uncover German plans to invade England from its North Sea islands, a coastal string that stretches from Holland to Denmark.

What raises the book from the routine and helped it become a classic—aside from being a ripping good story—is the author's belief at the beginning of the 20th century that in fact England did face the danger of a German invasion from across the North Sea, a danger for which the country was entirely unprepared. The Riddle of the Sands makes Childers's case for the danger using  fiction set in real places.

"Immensely popular in the years leading up to World War 1," writes the publisher of the 2018 reprint I read, "The Riddle of the Sands is a precisely drawn and geographically accurate adventure that . . . was perceived as so accurate, in fact, that it actually influenced the placement of multiple naval bases by Winston Churchill after its publication."

The novel follows Carruthers, a bored British Foreign Office clerk, who accepts an invitation to join his old friend Davies on a sailing trip through the treacherous waters of the Frisian Islands off the German coast. But what begins as a leisurely holiday quickly transforms into a tense investigation. Davies believes that German forces are secretly preparing for an invasion of England—and he needs Carruthers’ help to uncover the truth. Both are Cambridge graduates in their mid-20s. Carruthers speaks fluent German; Davies is a brilliant small boat sailor. As the two navigate shoals, fog, and suspicious naval activity, they stumble into a geopolitical conspiracy that would later echo the real fears and rivalries of pre-World War I Europe.

Childers writes from the inside. He had extensively sailed the waters he writes about and was himself a veteran of British intelligence. If you buy it, make sure the edition includes the five charts charts that support the story. Some readers may be put off by the 1903 British sentences, but they are no more complex than Conan Doyle's or Wilkie Collins's.

According to Wikipedia, Childers was a firm believer in the British Empire and served as a volunteer in the army expeditionary force in the Second Boer War in South Africa. His experiences there began a gradual process of disillusionment with British imperialism. He was adopted as a candidate in British parliamentary elections, standing for the Liberal Party at a time when the party supported a treaty to establish Irish home rule, but he later became an advocate of Irish republicanism and the severance of all ties with Britain.

On behalf of the Irish Volunteers, he smuggled guns into Ireland on his own sailboat that were later used against British soldiers in the Easter Rebellion. He had a significant role in the negotiations between Ireland and Britain that culminated in the Anglo-Irish Treaty, but was elected as an anti-Treaty member of the first Irish parliament. He sought an active role in the Irish Civil War (over the acceptance of the terms of the treaty) that followed, was arrested as a rebel, and was executed in 1922 by the Irish Free State.