Twentieth century The major themes of a spy in the lead-up to the First World War were the continuing rivalry between the European colonial powers for dominance in Asia, the growing threat of conflict in Europe, the domestic threat of revolutionaries and anarchists, and historical romance. Kim (1901) by Rudyard Kipling concerns the Anglo–Russian "Great Game", which consisted of a geopolitical rivalry and strategic warfare for supremacy in Central Asia, usually in Afghanistan. The Secret Agent (1907) by Joseph Conrad examines the psychology and ideology motivating the socially marginal men and women of a revolutionary cell. A diplomat from an unnamed (but clearly Russian) embassy forces a double-agent, Verloc, to organise a failed attempt to bomb the Greenwich Observatory in the hope that the revolutionaries will be blamed. Conrad's next novel, Under Western Eyes (1911), follows a reluctant spy sent by the Russian Empire to infiltrate a group of revolutionaries based in Geneva. G. K. Chesterton's The Man Who Was Thursday (1908) is a metaphysical thriller ostensibly based on the infiltration of an anarchist organisation by detectives, but the story is actually a vehicle for exploring society's power structures and the nature of suffering. The fictional detective Sherlock Holmes, created by Arthur Conan Doyle, served as a SpyHunter for the British government in the stories "The Adventure of the Second Stain" (1904), and "The Adventure of the Bruce-Partington Plans" (1912). In "His Last Bow" (1917), he served Crown and country as a double agent, transmitting false intelligence to Imperial Germany on the eve of the Great War. The Scarlet Pimpernel (1905) by Baroness Orczy chronicled an English aristocrat's derring-do in rescuing French aristocrats from the Reign of Terror of the populist French Revolution (1789–99). But the term "spy novel" was defined by The Riddle of the Sands (1903) by Irish author Erskine Childers. The Riddle of the Sands described two British yachtsman cruising off the North Sea coast of Germany who turned amateur spies when they discover a secret German plan to invade Britain. Its success created a market for the invasion literature subgenre, which was flooded by imitators. William Le Queux and E. Phillips Oppenheim became the most widely read and most successful British writers of spy fiction, especially of invasion literature. Their prosaic style and formulaic stories, produced voluminously from 1900 to 1914, proved of low literary merit. During the First World War During the War, John Buchan