As always, I’d like to take a few minutes to differentiate between fact and fiction in my stories. Many of the plot elements are drawn straight from history, though, of course, I fictionalized the players and attributed them to Drake and Margot rather than the actual historical figures who did them, some of whose names cannot be found now, thanks to documentation being destroyed after the war. For instance, the wolfram really was discovered in the warehouse in Bilbao when an agent claimed he was chasing a guide dog inside. By 1917, Gotha and zeppelin air raids over London had become quite common, and though destruction was minimal by World War II standards, it was nevertheless terrifying for the city’s occupants, who were still adjusting to the idea of danger coming from the skies. The raid at the end of my book is fictionalized, but it draws on the documented history of other similar raids. Other incidents like Hall sending a false “all mines have been cleared” message to the German minelayers did happen, though the dates have been tweaked slightly, as were a few others in regards to the Erri Barro and the U-boats caught skimming over their anti-sub nets, so as to fit neatly in my narrative. A codebook really was recovered from a zeppelin that crashed when its pilots suffered altitude sickness, though it happened a few months earlier than I said. And Hall truly did have his codebreakers create a fake “Emergency Code” that he deliberately put into enemy hands—sold it to the enemy, in fact, for five hundred pounds, though he never sent a message in it for them to “intercept.” I thought it would be fun to include the code briefly in my story though.

One of the greatest challenges of those who ran Room 40 was finding ways to preserve their secrecy and yet still give their leaders the information they needed to make the war go in their favor. Their decisions were constantly based on whether sharing certain information would reveal their hand to the Germans. And so, though they knew about nearly all attacks and raids before they happened, they couldn’t always do anything about it. They had to first have a cover story for how they could have found it out . . . which is why Admiral Hall frequently used the identities of German agents he’d arrested to send misinformation to Germany.