A brief history of secret British and American World War II organizations, their training, tools, successes, and their legacy. Winston Churchill famously instructed the head of the Special Operations Executive to “Set Europe ablaze!” Agents of both the British Special Operations Executive and the American Office of Strategic Services underwent rigorous training before making their way, undetected, into occupied Europe to do just that. Working alone or in small cells, often cooperating with local resistance groups, agents undertook missions behind enemy lines involving sabotage, subversion, organizing resistance groups and intelligence-gathering. SOE’s first notable success was the destruction of a power station in France, stopping work at a vital U-boat base. Later operations included the assassination of Himmler’s deputy Reinhard Heyrich and ending the Nazi atomic bomb program by destroying the heavy water plant at Vemork, Norway. OSS operatives established anti-Nazi resistance groups across Europe, and managed to smuggle operatives into Nazi Germany, including running one of the war’s most important spies, German diplomat Fritz Kolbe. All missions were incredibly dangerous and many agents were captured, tortured, and ultimately killed—the life expectancy of an SOE wireless operator in occupied France was just six weeks. In this short history, historian James Stejskal examines why these agencies were established, the training regime and ingenious tools developed to enable agents to undertake their missions, their operational successes, and their legacy.