Anthony Doerr’s second novel chases two smart, unlucky children across wartime Europe through a vast, untidy plot. Marie-Laure LeBlanc goes blind at the age of six, but she learns to navigate her Parisian neighbourhood by studying a detailed model constructed by her father. Werner Pfennig, an orphan in a German mining town, has a prodigious curiosity: Why doesn’t glue stick to the inside of the bottle? Can magnets affect liquids?

Unfortunately, they live in circumstances that may not reward precocity, or may reward it in ambivalent ways. Werner’s knack for building radios sees him expedited through a training program for the Hitler Youth. Meanwhile, the Führer’s minions are hunting a diamond possessed by the Museum of Natural History in Paris. The Museum has three facsimiles made; they keep one and send the other two and the original off in all directions. None of the...