It is June 1941, and the low point of the war. England throws wave after wave of bombers across the Channel, but somehow the Lufwaffe is able to shoot them down at will. The skies - indeed the war itself - seem to belong to Hitler.
But on a small Danish island across the North Sea, Harald Olufsen, a bright eighteen-year-old with a talent for engineering, stumbles across a secret German installation. Its machinery is like nothing he has ever seen before and he knows he must tell someone - if he can only figure out who.
With England preparing its largest aerial assault ever, what Harald has discovered may turn the course of the war - but the race to convey the information could have terrible consequences for everyone close to him.
For his older brother Arne, a pilot in the grounded Danish Air Force and already under suspicion of the authorities. For Arne’s fiancee, Hermia, an MI6 intelligence analyst desperate to resurrect the foundering Danish resistance. And most of all for Harald himself - because as the hour of the assault approaches, it will all fall to him and his friend Karen to get the word to England.
And the only means available to them is a derelict Hornet Moth biplane abandoned in a ruined church, a plane so decrepit that it is unlikely ever to get off the ground.
Pursued by the enemy; hunted by collaborators; with almost no training, limited fuel, and no way of knowing if they will survive the six-hundred mile flight, the two will carry with them England's best - perhaps only - hope of avoiding disaster.