The mystery, or I should say the mysteries, begin when Bernard is asked by a wealthy Frenchman to design hiding places in apartments for Jewish individuals. Bernard, who was raised by parents who hated Jews, feels rather indifferent about them, but likes the idea of outwitting the Nazis. He is fully aware of the risks he is taking and the constant fear that will accompany him once he becomes involved in the projects.
The first mystery begins: Is he going to survive or get caught and endure the torture the Nazis will inflict on him?
The projects also come with a considerable amount of cash and the chance to design a factory for the Germans outside of Paris. The second mystery unfolds: Will Bernard become an accomplice of the German Reich, a collaborator?
One of the hiding places is behind the brick wall of a fireplace. When the Nazi’s storm the apartment without finding the Jewish couple they are looking for, they burn the apartment down. The couple is smothered to death as Bernard did not anticipate such a situation and has failed to build an air pipe for them. His failure initiates the third mystery: After this tragic error, will Bernard begin reevaluating the choices he has made?
The novel slowly creates these moral dilemmas: Does designing factories for the Germans conflict with creating safe places for Jews? And how can a person who is devoted to France and has fought for its survival, collaborate with the enemy who is occupying his country?
With the death of the Jewish couple, Bernard begins to see things differently, he realizes the occupation brought out the very worst in human beings, the hardships had set one person against another, one group against another, neighbor against neighbor, friend against friend. What he was doing for the Germans was simply wrong.
Lucien knew he couldn’t be that way and just stand by; he had to continue what he’d been doing. When he asked himself why he was risking his life, the answer wasn’t the cash, the factories, or the sheer thrill of the challenge. He was risking his life because it was the right thing to do. He had to go beyond himself and help these people.
He had also fallen in love with a woman who was hiding two young children and had admired his growing moral conscience. Then a young boy, who he had taken in to both his home and his workplace when the Nazi’s killed his parents, saved his life.
The five of them become a “family” that eventually escapes to Switzerland, oddly with the help of a Nazi who had come to admire Bernard’s work and had found pleasure in their mutual appreciation of European art and architecture.