Just before summer begins, thirteen-year-old Ali finds an old photograph. She recognizes the two children in it; one's her mother, the other her aunt Dulcie—but who is the third person, the one who's been torn out of the picture? Ali will have two months to figure it out, since she's spending the summer with her aunt and her cousin in the same house her mom and aunt used to visit when they were kids.

Then Ali meets Sissy. Sissy is mean, spiteful, and determined to ruin Ali's summer. Sissy also has a secret. Could it have something to do with the old photo? Ali is dying to find out—though, if she's not careful, that may be exactly what happens to her.