Sarah feels lucky to have such a fun, happy mother. Her best friend Robin's mother is suffering from clinical depression and rarely leaves the house. This causes Robin to act out by engaging in risky behavior like walking on a ridge on Sarah's roof and planning to perform a dangerous stunt at the school gymnastics show.
Sarah's luck soon runs out when her mother becomes ill with advanced melanoma. Both Sarah and her parents go through periods of anger and denial. There comes a time when Sarah's mother is sure she can beat the cancer and the family has a Christmas party for all their friends.
The good times can't last, however, and Sarah's mother is rushed back to the hospital. Sarah tunes out what is happening by ignoring the ringing phone and going to Robin's house while her mother is being admitted. While at her friend's house, Sarah learns that Robin's mother not only suffers from depression, but from agoraphobia and other fears as well. (She seems to have some anxiety that Sarah is there...This author was pretty cutting edge. Another one of her early books mentioned the "fainting game" that kids play to get high.)
Because of the uncertainty she feels about her own parents not attending the gymnastics show, Sarah plans her own risky stunt (jumping from the top of the ropes to the trampoline), but the girls cancel their plans when both sets of parents show up in the audience at the last minute.
The book reaches its tearful conclusion as Sarah's mother gets weaker and eventually dies on Christmas Eve. The dying scenes are quite emotional, with Sarah yelling in anger at what is happening and her parents equally upset. After her mother is gone, Sarah's father reveals that she had been writing in a diary for Sarah to read. An epilogue taking place a few months later finds Sarah reading the book and taking care of a new kitten.
Sarah's mother might have been a little more memorable had she not been quite so perfect, but the book was still pretty sad for a kids' book.