Camille Prescott has it all. A doting husband, two children, a charming home in a seaside enclave, and a beautiful, fixed smile that exudes normalcy. But behind her polished mask lurks a much different Camille - one with a padlocked vault of secrets. Raised by a vindictive and psychotic woman, Camille has gone to great lengths to bury her past and for good reason: if her mother ever finds her, she will kill her.

But nothing can prepare Camille for the day her six-year-old daughter, Georgie, starts showing signs of unsettlingly familiar behavior, including an imaginary new friend who casts a disturbing influence on everything the little girl says and does. Worse than that, Georgie's imaginary friend knows things about Camille's childhood, things Camille has never told a soul. Is it a coincidence or is Georgie's imaginary friend not so fictional after all?