Anna Klein is ready to return to work as a literary agent for the first time since having children. She and her husband, Josh, decide to hire a live-in nanny with some trepidation, but all their misgivings disappear as soon as they meet Oaklynn Durst. She has stellar references, a calm disposition and a natural way with children. Not to mention their kids simply adore her. But not long after Oaklynn arrives, the children start to come down with the most puzzling illnesses and inexplicable injuries. When the maternal Oaklynn is there to comfort everyone, Anna can’t help feeling a little eclipsed. And suspicious. Her husband and friends assure her that her anxieties are getting the best of her – Oaklynn is perfect. But Anna’s not so sure … As she delves into Oaklynn’s past, she discovers too late that the woman who has been living in her house is not at all who she claims to be. But Oaklynn’s not the only one who has been lying. And when everyone’s dark secrets are forced into the light, the consequences may just turn deadly.