The Devil's Arithmetic is a VERY disturbing book. It is about a Jewish
girl who doesn't appreciate her grandfather and his resentment towards
concentration camps. She thinks he just goes on and on, and shouldn't
overreact so much, even if he was in one.
She is at his house for Passover (Pesah) and goes to open the apartment
door to let the spirit of Elijah in. However, when she opens the door,
she sees a field, and when she turns around she finds herself in
pre-WWII Poland.
When she goes to a wedding, they are arrested by the Nazis and shipped
off to a concentration camp. It's about living in a concentration camp
as her great-aunt's best friend.
Part of the fact that it's disturbing is because of the detail, and
part of it is because you can never tell if she's going to live or die.
You can read it and find out, but I wish I had waited a little longer.