This book does a good job of describing the intrigue and danger of the world of spies in Warsaw shortly before the beginning of World War II. The reader of today knows what's about to happen, but the characters in the book are not so blessed. The characters in the book are pretty sure that war is coming, but they have no idea of when or where. According to this story a clever spy for the French is able to piece together evidence of how and where the Germans plan to attack France. But according the this story the evidence is disregarded because it was thought to be misleading information purposely planted by the Nazis.
I have no idea if there are any true historical indications that French intelligence had this kind of information. However, it is a historical fact that the French believed that the fortifications of their Maginot Line would sufficiently delay any German invasion to permit mobilization of French reserves. Based on their experiences from World War I, the Maginot Line seemed to be a good plan. From our perspective looking back we know that it was another example of making plans to fight the past war. At the time nobody knew for sure what the future held.