OSS Major Jeffrey Hunter is seconded to Colonel Nigel Patrick. They seem to be running a film company. In reality they're working on the Normandy invasion. Their unit leaks information like a sieve. It's meant to. They're trying to convince the Germans that the invasion will take place, at least in part, in the Netherlands. If the Germans believe this, they'll station divisions far from the actual invasion. Among the people they think is a German spy is Dutch Annemarie Düringer. Has she caught onto the game they're playing?
Even though the War years kept warning us about German propaganda and German spies -- who seemed to wander about the landscape without anyone noticing what they were doing -- there seems to be little doubt that the British played both games much better. At least some of the claims about German atrocities were not believed because they seemed to be repetitions of what had been said during the Great War. It was only after the war that the exploits of British Intelligence like this and THE MAN WHO NEVER WAS began to surface, and even longer for it to turn out that Ian Fleming was an insane operations runner.
It's a standard but well executed espionage thriller, even though it takes almost a third of its length to start moving.