Part of the Holocaust’s unknowability stems from its origins. Stone points in particular to the role of ideology in spurring the mass murder. We know well, naturally, that Adolf Hitler and other leading National Socialists were rabid antisemites. Hitler’s infamous autobiography Mein Kampf is an antisemite’s manifesto and Nazi propaganda was replete with antisemitic stereotype. But Stone insists that there is something unknowable or even mystical in the role that antisemitism played in Nazi thought. It was not merely “a logical outgrowth of Nazi eugenics,” he contends. Rather, “it grew from a mystical notion of ‘thinking with the blood’,” what the great Holocaust historian Saul Friedländer termed redemptive antisemitism: the notion that the “Aryan” race’s salvation lay in the extermination of Jewish people. The significance, to Stone, is that such hatreds do not have logical origins, nor can they be combatted with reason. For our own world, increasingly characterized by misinformation, “fake news,” and conspiratorial thinking, it is a troubling conclusion.

There is also a longstanding mystery over when, precisely, Hitler and the rest of the Nazi leadership determined to murder all of Europe’s Jews. Historians have long shown how the Holocaust evolved in stages: from discriminatory legislation in the 1930s, to the pogrom known as the Night of Broken Glass in 1938, to ghettoization and the mass shootings of Eastern European Jews in the early 1940s, to finally the industrial extermination camps that opened their gates in late 1941 and early 1942. It’s that last stage—the camps where Jews were murdered with poisonous gas—that has become the most iconic in our image of the Holocaust. The move from mass murder by bullets to mass murder by gas is also what countless historians have grappled with, trying to explain how, why, and when precisely the decision was made.

The mystery stems from the fact that the Nazis were careful about cleaning up their paper trail. Surviving documents employ euphemism in a vain effort to hide their true import. It also comes from the fact that Hitler notoriously detested writing down his orders, preferring to transfer commands orally to his top lieutenants. Thus, historians have never found a written Führer order commanding that Jews be deported to and murdered at the six extermination camps of Eastern Europe. Instead, scholars have had to painstakingly reconstruct more circumstantial evidence, such as notes about what Hitler said at various gatherings of leaders. On December 12, 1941, for instance, he told officials, “The world war is here, the destruction of the Jews must be the inevitable consequence.” These sources have led historians to conclude, as Peter Longerich writes in his recent biography of Hitler, that “it is clear that it was always he who set the agenda for the various stages of radicalization and controlled developments.”