This book is written from a naive 9 yo boy's perspective. He comes home from school and is upset to find the maid packing his things. They move from Berlin to a new house far away as his father got a promotion. A tall fence separates thin people that live on the other side of the fence from his house. The boy ends up befriending a boy on the other side of the fence.
The author intentionally makes it so the boy is one of the few (including the reader) who doesn't know what is going on. You have to go with the premise that a 9 yo boy wouldn't understand all of the things in this new environment when he is living in WWII and his father is a Commandant in the Gestapo (this apparently was a stumbling block for a lot of people). I enjoyed this book a lot and have gotten it for my young niece to read.