Since childhood, Lila has been closer to her twin brother Billy than anyone in the world. They even took a vacation together when Lila and her husband Patrick got tenure. To Patrick, his wife's relationship with her twin has always been something of a mystery. He knows Lila and Billy's parents died when they were teenagers, but he doesn't understand why Lila never talks about her parents. He also doesn't understand why books have always been so crucially important to the twins. A math teacher, Patrick is particularly mystified by Lila's obsession with stories.

Then one afternoon, Billy points a rifle out the window of a hotel across from an elementary school. Billy is shot, "suicide by police," Lila is told. Billy's death devastates her, but it his reason for wanting to die that both stuns and horrifies her: he'd been charged with child abuse, of endangering the life of his middle child and namesake, eight-year-old William.

In the aftermath of her twin's death, Lila falls apart. Soon her job, her marriage, her carefully constructed past-and even her sanity-are put at risk, as she tries to make sense of her life with Billy and the long-buried secrets of their childhood. While Patrick attempts unsuccessfully to save his wife, Lila's slowly comes face to face with who her brother really was-only to realise that there may be another person in danger now. Billy's favourite child, her nephew William, may be about to re-enact the same story Billy taught her to believe in so many years ago: a story of betrayal and lost innocence that must be redeemed by a violent act that could destroy them all.