I think that maybe you are having trouble finding a summary because the book is not a fiction book. It describes the stages of grieving that a persons goes through after they lose a loved one or find out that they are dying due to a terminal illness.
The stages are :
Kubler-Ross noted that people do not always follow these in order and they also may not experience all of the steps but they will experience at least two. Her goal was to make people aware of the difficulties that people experience when they are going through a traumatic experience.
I have posted a link below that discusses the cycle in detail. Hopefully this can help you get started.