Let me say from the outset, that I wouldn't have chosen this book for my recreational reading--I'm leading two book discussions on it in the spring. My review is based solely on my personal observations and preferences (which I'll work consciously not to inject in the book discussions).
The story is about Irene, Gil, and their three children. Irene discovers that Gil has been reading her diary; so, she decides to write entries that will upset/hurt Gil in the diary he has found, while writing truthful entries in a diary she keeps in a safe deposit box. The entire book is comprised of the hurts (physical and emotional) that Irene and Gil enact on each other and the children. This is why I wouldn't have chosen the book for myself--it's just too traumatic. I'm very protective of my limited and precious reading time.