In this twisty, mind-bending thriller from the bestselling author of Behind Her Eyes, Emma Averell worries that her crippling insomnia is a sign that she’s slowly going insane—like the mother she’s worked so hard to leave in her past.

Emma Averell loves her life—her high-powered legal career, her two beautiful children, and her wonderful stay-at-home husband—but it wasn’t always so perfect. When she was just five years old, Emma and her older sister went into foster care because of a horrific incident with their mother. Her sister can remember a time when their mother was loving and “normal,” but Emma can only remember her as one thing—a monster. And that monster emerged right around their mother’s fortieth birthday, the same age Emma is approaching now.

Emma desperately wants to keep her successful life separate from her past, so she has always hidden her childhood trauma. But then she’s unable to sleep, and now losing time during the day, also one of the first symptoms her mother showed. Is the madness in her blood, just as her mother predicted? Could she end up hurting her family in her foggy, frenetic state? Or is she truly beginning to lose her mind?