Dr. Carter Nix is a respected child psychology. His wife, Jenny, becomes concerned that Carter is obsessively studying their daughter, Amy; he regards her like a scientist tracking the development of his creation. But Carter himself suffers from multiple personality disorder; his alternate personalities include Cain, a violent petty criminal, Josh, a shy 7-year-old boy, and Margo, a middle-aged nanny who protects the others at all costs. Carter and Cain are killing young mothers to procure their children, apparently for experiments performed by Carter's father, a child psychologist who lost his license years earlier after performing unethical experiments on children.