Behind the front lines of the Second World War raged a different kind of battle. In secret camps across Britain, thousands of enemy spies, soldiers, and war criminals were interrogated in the effort to defeat Nazi Germany and the ideology that drove it. Drawing on extensive British archival sources, Artemis Photiadou uncovers the methods, motives, and moral tensions behind this vast machinery of questioning. Within it, officers, scientists, and linguists sought to extract military intelligence, as well as to grasp why individuals fought Hitler's war and, eventually, to assess their complicity in the regime's crimes. The resulting interactions expose the complexity of those who were questioned, the assumptions of their interrogators, and the ethical contradictions of a liberal state at war. This is a vivid account of how Britain attempted to comprehend the enemy it was fighting. This title is also available as open access on Cambridge Core.