Will Flowers doesn't understand what could have happened. His sister, Estelle, used to be really cool. She was quiet, responsible, and most times you'd never even know she was around(which was the cool part). But lately, Estelle has been acting totally weird - to everyone. All she does is get mad and yell. She yells at Mom. She yells at Dad. She even yells at little Muffy. But mostly she yells at Will. And when Estelle yells, everyone listens! Will thinks Estelle is just going through a weird stage, but what if she stays this way - FOREVER?