There is no evidence that there was ever a Lorenz machine installed in the Ritz Hotel in Paris—that is pure imagination on my part. However, there is certainly evidence that the Nazis housed cipher machines in other hotels and buildings used as headquarters. An objective of the disastrous 1942 Dieppe assault may have been to capture coding/cipher technology at the Hotel Moderne, according to author David O’Keefe. Knowing that the Paris Ritz Hotel served as the headquarters of the Luftwaffe and was the residence of Hermann Göring (who was tapped as the successor to Hitler), a need for a direct, protected line of communication to the Führer seemed plausible for this work of fiction.

There is also no evidence that Bletchley Park ever received any intelligence from SOE operatives such as photos, codebooks, or even sketches of the Lorenz machine. Declassified documents from the Target Intelligence Committee (TICOM), which was a joint operation between the U.K. and the U.S. targeting the capture of German signals intelligence organizations, provide the first Allied description of a captured, intact Tunny communications train, but not until 1945, long after D-Day. Nazi Field Marshal Albert Kesselring’s captured “Fish Train” included six German trucks housing Tunny machines, radio transmitters, receivers, and encryption devices. Each truck contained two bunks for the driver and assistant, who operated the equipment. Tutte and his team did not have the benefit of this information at Bletchley. All the decryption work done was the product of an astonishing feat of reverse engineering.

The first Colossus machine, developed by Flowers, was operational by December 1943, allowing the Allies to intercept and decode critical information leading up to and after D-Day. For this story, however, I chose to imagine that Bletchley and its brilliant minds might have had a helping hand.

The Paris Ritz Hotel, with its socialites and industrialists, collaborators and spies (and, yes, hidden cupboards and stairways), remained the glamourous headquarters of the Luftwaffe throughout the war. The Charles Le Brun painting The Sacrifice of Polyxena (currently hanging in the Metropolitan Museum of Art, New York) that I have used in this book was, in fact, discovered hidden in plain sight in the luxurious Coco Chanel suite prior to the hotel’s recent renovation. The provenance for this painting before its discovery in the hotel remains unknown. The current theory is that when César Ritz purchased the hôtel particulier at No. 15, Place Vendôme, once the home of princes and dukes, the Le Brun canvas was already hanging within. I chose a different history for this painting.