One twin vanished. The other twin remained. Until now...

No one knows why Lucy's 14-year-old daughter Eden almost drowned in the lake after school one day. But now she’s safe and well. Lucy can start being a good mother. The mother she should have been all these years—years that were fraught with grief over the loss of Eden’s twin during pregnancy.

Yes, all that matters is Eden is fine. But then Eden starts saying Eden isn’t her name. Her name is Eli. The name Lucy had reserved for Eden’s unborn twin. Don’t worry, says the doctor. Eden is completely fine, says her husband. Of course I’m fine, Eden says, with that strange new smile of hers. I didn’t die. I’m here.

But Lucy knows something’s very wrong with Eden. She’s not her maddening, complicated teenage girl anymore—this straight-backed, even-tempered, steady-eyed child in her house is someone else entirely. Eden, it seems, is the twin who disappeared…