Esther lost her husband, Julian and her children, Harriet and Dexter, in a car accident and is struggling with her grief. Spurred on by her own loneliness and a need to make amends for not being able to save her own children, Esther takes it upon herself to watch the woman who lives at number 19. But when inexplicable incidents begin to happen in Esther’s house, she begins to fear for her safety. Meanwhile, over at number 19, the woman’s behaviour is becoming more explosive and unpredictable. As Esther starts to lose her grip on reality, her world begins to unravel. Just who is this strange woman at number 19? And why is Esther so obsessed with her?