Sarah is having an existential crisis. Sarah is 16 years old. Sarah is 10. And 22. and 40. She is many Sarahs. She is a mix of needs and worries and crises and traumas. 
 To say anything more specific about this is... not really possible. There's the absent brother and the mystery of why he left. There are the parents who hate each other. And there's why Sarah has refused to go to school and where she goes instead, and how her older and younger selves are also hanging around. In short: this is an AS King novel, and you just need to get into the groove of it and let the surreal brilliance wash over you.