This is the story of a German spy during the Second World War who discovers a secret plan by the British government to wrong-foot the Germans into thinking that the operation to liberate France and north-west Europe would land at Calais rather than Normandy. The story itself is fiction but the plans were real, giving this a solid grounding in fact.
The book benefits from being relatively short and keeping the pace up all the way through. It features a strong female character, which is refreshing.
I had heard that this is one of the great spy stories, up there with The Day of the Jackal. I don’t think it comes close but it is a good thriller.