Atlee Pine has a memory stuck in her mind like a steel splinter: she is six years old, and a man who invades their home uses a nursery rhyme to choose between her and Mercy, her twin sister. In the end, he settles on Mercy and takes her away with him. Atlee never saw her sister again... Now, thirty years later, FBI special agent Pine is going to a high-security prison, where a particularly dangerous maniac killer who has admitted to many crimes is serving a life sentence. Atlee recognized him. He was the one who came to their house an eternity ago. And now she wants to ask him just one question: “Where is my sister?”