Wars are brutal. Often the common people bear the brunt of it for no fault of theirs. People are killed, women are raped. All the light we cannot see, portrays all this and more. The title itself portrays the fact that one doesn't often see the true picture.
Marie Laurie is a blind girl. She lives in France with her father. Her father is a locksmith in the Natural History museum.
Wesner is an orphan who has a sister named Jutta, lives in Germany. He is a bright boy, keen learner who takes a lot of interest in radios, its components and signals. He gets recruited in the army.
Although Werner is  German, he still comes to rescue a French girl Marie.
All war stories are usually heart rending.  Two struggling youngsters meet due to radio transmissions.
I commiserate with the character Frederick. A person with so much knowledge about birds get bullied to such an extent that he ends up with a  memory loss.
This book is a must read.