The big idea here is that Rose Edelstein can taste emotions in food, specifically the emotions of the people who made the food. This is a pretty traumatic discovery for her, especially since it takes place when she is 9. Much of the book deals with her ways of coping with and finally learning to deal with her "gift."
Rose is not only in her misery - each member of her family is off in some way, from the flat-out strangeness of her brother Joseph to the intense need of her mother and the mostly vacant spot that is her father. Luckily, the claustrophobic feel of the family is broken up from time to time by Joseph's only friend George, who serves as an anchor to reality throughout the book.
I said it was a big idea and these are crazy characters but this isn't a big book in temperment. It's a small book, concerned with everyday discoveries about ourselves and the world around us. That's not a bad thing.