David M Thomas 
The Schneider Papers [EPUB ebook] 

1936: Harald Mason, a German-born naturalised British airman, is sent by a concerned Foreign Office to Berlin to unearth Luftwaffe expansion plans and investigate the sustainability of high-octane aviation fuel supply in time of war. Werner Scribner, a technical draftsman at the new Luftwaffe Air Ministry in Berlin, is determined to bring down the Anti-Christ Hitler.
A narrative of disparate characters, from the leonine intelligence chief Major Alastair Cartwright MC in London to the clever and elegant Elisabeth Schneider, economist and Soviet spy, this is a story of American business funding Nazi Germany and the rebuilding of Soviet Russia, as part of President Franklin D. Roosevelt’s New Deal programme.