Throughout the novel, Harris gradually explains, in a fictional backstory, the developments that allowed Germany to prevail in World War II. The author explains in the "Author's notes" that except for the backstories of the fictitious characters, the narrative describes reality up to 1942, after which it is fictional. A significant early point of divergence is that Heydrich survived the assassination attempt by Czech fighters in May 1942 (he was killed in reality) and later became head of the SS. The Nazi offensives on the Eastern Front ultimately push back the Soviet forces, with the Case Blue operation succeeding in capturing the Caucasus and cutting the Red Army off from its petroleum reserves by 1943. The Nazis also found that the Enigma machine code had been broken. A massive U-boat campaign against Britain then succeeded in starving the British into surrender by 1944.