The English air

In this unlikely story Wynne, an English girl, meets her half-German cousin Franz when he visits England in 1938. Franz is doing undercover research for his Nazi father, using his English relatives as a cover. Wynne and Franz fall in love. He has to go back to Germany but is soon disenchanted with Nazism. He joins an underground group working against the Nazis. Eventually he escapes to Scotland, is injured and ill for a long time. He tells all his secrets to Wynne's Uncle Dane who happens to be something in British Intelligence or whatever they called it. Franz, now Frank, and Wynne become engaged and Frank goes over to fight for Finland against the Germans. Everyone lives happily after ever.