Le Queux was the first and most prolific of all British spy writers, but Spies of the Kaiser was not just another tale of scheming foreigners and plucky British heroes, for this paranoid tale of German secret agents plotting the invasion of Britain played a major part in the formation of MI5, Britain's counter-espionage organisation. In his introduction, intelligence historian Nicholas Hiley explains how Le Queux's powerful blend of fact and fiction inspired a whole generation of British secret service officers, and led MI5 in a nation-wide hunt for a non-existent enemy.