This book by Ben McIntyre sets out the story of the 'double cross system' where spies who the Germans thought were working for them, were actually working for British Intelligence.
Although a work of non-fiction, it reads like a gripping adventure yarn.
The central claim of the book, is that the culmination of the deception was that the German military where misled into thinking the D-Day landings were a division for the 'real' invasion planned for Calais. This is both undoubtedly true and also meant that many lives were saved and that WWII ended sooner than it might otherwise have done.
It is heartening in a way to read of the often deliberate incompetence of many Germans working for the German intelligence services. Resistance to the Nazi regime could take many forms.
The bravery shown by those of the agents that flitted back and forth between England and occupied Europe is extra-ordinary.
McIntyre paints them all as complex and often flawed individuals - who never the less did extraordinary things. Some of the stories seem almost beyond belief, as has been said, fact is often stranger than fiction.