Caro Mitchell considers herself an only child--and she likes it that way. After all, her much older sister, Hannah, left home eight years ago, and Caro barely remembers her. So when Caro's parents drop the bombshell news that Hannah is returning to live with them, Caro feels as if an interloper is crashing her family. To her, Hannah's a total stranger, someone who haunts their home with her meek and withdrawn presence, and who refuses to talk about her life and why she went away. Caro can't understand why her parents cut Hannah so much slack, and why they're not pushing for answers.

Unable to understand Hannah, Caro resorts to telling lies about her mysterious reappearance. But when those lies alienate her new boyfriend, friends, and put her on the outs with her parents, Caro seeks solace from an unexpected source. And as she unearths a clue from Hannah's past--one that could save Hannah from the dark secret that possesses her--Caro begins to see her sister in a whole new light.