Additionally, the dates of his stress-related hospitalization differ slightly in my book, as his actual admittance was February 20, 1943, and his discharge June 2. Without specifics to draw from, my depiction of the inciting incident was solely my estimation. During his time at Woodside Officers’ Hospital, aside from starting to compile a chronology of his MI9 gadgetry—presumably for the autobiographies he eventually published—he expressed in a letter feeling “broken spirited” and “confined in this prison” to Norman Watson at John Waddington Ltd. Sadly, I surmise the missive wasn’t a facade to continue his duties behind the scenes, yet in light of his obsession with his war work and his alleged (if denied) application later to serve the SOE, I like to think he’d have gladly persisted if given the opportunity and the right partner. The codes used for maps, incidentally, did include one referred to as “Dutch girl,” which for me was just too fitting not to include.

When needed for narrative drive, I admit to entirely ignoring lunar cycles and giving myself wiggle room on nighttime visibility—because, yes, blackouts can be very, very dark. Also, I took liberties with Utrecht’s tram access and routes and occasionally condensed timelines for pacing, most notably in the grim fallout at Bethnal Green station, as well as with Fenna’s insertion and night-drop training. Granted, to be fair about the latter, I’ve had the great pleasure of listening to enough anecdotes from World War II veterans through the years to know that despite what was standard, there were always remarkable and necessary exceptions. It was wartime, after all.

In other areas of the novel, Houdini’s Big Little Book of Magic (minus “& Stunts”) indeed exists, though it focuses on close-up magic, not escalating to the showier tricks and escapes featured in his other books. As for words of note: I often referenced the Netherlands by the more period-colloquial (versus technically geographical) name of “Holland”; since Engelandvaarders doesn’t have an exact translation in English, I chose “England paddlers,” though it is often defined as England farers or sailors; and while cemetery more accurately applies to the setting of the gadget bunker, I used graveyard interchangeably due to Hutton’s consistent use of the descriptor. Plus, let’s be honest—it’s a cooler, creepier word.