Can someone come back from the dead?

It all starts with a torn photograph, tucked in a Nancy Drew mystery, that 13-year-old Ali finds, as she is digging through a box of old books from her grandmother's house. It's a picture of her mother, her aunt and someone else.  Just an arm shows in the picture and on the back of the photo someone has written Claire, Dulcie and T....  Ali heads to the kitchen to ask her mom about the mysterious T and suddenly her mom is shrill and tense and slamming her bedroom door with a headache.  

Ali's life turns when her Aunt Dulcie shows up to ask if Ali can come to the old cabin in Maine to watch her young cousin Emma this summer.  For Ali this is a chance to escape her mother's control.... a chance to breathe and explore the world.  Mom and Aunt Dulcie are quick to say neither one of them can remember the other girl in the photograph.  Why?  

Ali finds herself spending the summer at the old house by the lake where her mother had always vacationed as a child. She's there with her aunt and her cousin, Emma. Ali is hoping to solve the mystery, and one day a new girl, Sissy, shows up.  Sissy with her anger and her spitefulness, casting a shadow on the summer days and exuding mystery with every step and every word. Where does she come from?   Who is Sissy, and who was the third person in that photograph?