Three years ago, Isabelle and Agatha Lawrence went swimming alone, after their father had told them not to. Three years ago, Agatha died. Three years ago, Isabelle told a lie she had to hold on to ever since. But now Agatha's back. And she's out for blood. So now, with her dead twin sister haunting her, ten-year-old Isabelle has two choices: she can tell her family what really happened that night, or she can face the consequences. But the truth, sometimes, can be more dangerous than lies.