13-year-old Ali is thrilled to be spending the summer at the lakehouse with her aunt Dulcie and Dulcie's adorable 5-year-old daughter Emma, rather than being stuck at home with her moody mother Claire. Fifteen years ago, something terrible happened at the lakehouse, something that caused a rift between Dulcie and Claire, something neither of them will speak of. The only clue is an old torn photograph and a vicious little girl named Sissy, who wants to lure Emma into the deep, dark, dangerous lake. To save Emma, Ali must learn both Sissy's secret and her own mother's.