While conducting research for this book, I became captivated by a 2012 British news report about the skeletal remains of a war pigeon that was found in a Surrey chimney, decades after the war. Attached to the pigeon’s leg was an encrypted message, which would baffle GCHQ code breakers for years. The mystery of this war pigeon and its indecipherable message served as inspiration for writing this story.

During my fact-finding, I also became increasingly fascinated by the extent pigeons were used in World War II. The National Pigeon Service, a volunteer civilian organization in Britain, delivered some 250,000 war pigeons to British Services between 1939 and 1945. Source Columba was the actual code name for airdropping 16,000 homing pigeons in German-occupied France and the Netherlands as a method for locals to provide intelligence to Britain, such as troop movements. I imagined Susan and Bertie to be dedicated members of the National Pigeon Service who believed that their extraordinary birds would help Britain survive.

In addition to war pigeons, I was intrigued to learn that over 200 volunteer American pilots served in the Eagle Squadrons of the Royal Air Force, prior to the United States joining the war in December 1941. These brave men made their way to Britain, usually through Canada, disregarding US Neutrality Acts. Charles Sweeny, a wealthy Londoner, and Billy Bishop, a Canadian World War I air ace, played significant roles in recruiting American volunteer pilots for the RAF. I envisioned that someone like Ollie, a crop-duster with British ancestry, would have the skills and motivation to join the fight.

During my research—in particular on the early stage of World War II—I discovered many compelling historical events, which I strived to accurately weave into the timeline of this tale. For example, Epping’s Sprigg’s Oak Maternity Home was bombed on October 9, 1940, killing eight expectant mothers who were seeking a safe place outside the city of London in which to deliver their babies. The destruction that Ollie finds when he arrives in Britain is the result of the bombings in Liverpool, specifically the Cleveland Square shelter, which took a direct hit, resulting in the death of at least sixteen civilians. Also, the Luftwaffe conducted numerous raids on North Weald Airfield in 1940, one of which I used to launch Ollie into German-occupied France. Additionally, I attempted to accurately reflect the various types of aircraft that were used by British and German forces during the early stage of the war, as well as the various equipment and pigeon-raising methods utilized by the National Pigeon Service. Any historical inaccuracies in this story are mine and mine alone.