Sam Waver has always idolised his big brother, Jason. Unlike Sam, Jason, seems to have life sorted - he's kind, popular, amazing at football, and girls are falling over themselves to date him. But then one evening Jason calls his family together to tell them that he's been struggling with a secret for a long time. A secret which quickly threatens to tear them all apart. His parents don't want to know and Sam simply doesn't understand. Because what do you do when your brother says he's not your brother at all? That he thinks he's actually . . . your sister?