The time is 1941, and British bombers attacking Germany are being blown out of the sky in horrific numbers. How do the Nazis know they're coming? The answer is an infant technology called radar, and the Brits--with help from the Danish Resistance--must figure out how and where the German radar stations operate.
Harald Olufsen, a brainy 18-yearstumbles across a German installation by chance, realising its importance when he meets a member of the early Danish resistance. Harald find a tiny wood-and-linen biplane called a Hornet Moth, half-rotted and stored away in a Danish barn, at the home of a school friend. Then, when the very outcome of the war begins to turn on Harald getting a certain roll of film from Denmark to England, he remembers it, and luckily his friend's twin sister is able to fly it.
It includes some predictability and also some twists - I found it difficult to put down, as is usual with Ken Follett books