The woman at number 19Esther lost her husband, Julian, and her children, Harriet and Dexter, in a car accident and is struggling with her grief.
Her only friend is Amy, a young lady who lives close by and visits Esther to keep her company.
Esther’s sister, Charlotte, also visits from time to time but Esther despises her. She believes that Charlotte had an affair with Julian and was planning to run off with him and the children on the same journey that killed her family and left Charlotte seriously injured.
From her window, Esther watches her new neighbour and becomes concerned about the erratic and abusive behaviour she displays towards her husband and children.
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 and keep a record of her cruelty with a mind to reporting it to the authorities.
When unexplainable incidents begin to happen in Esther’s house, she begins to fear for her safety and as more and more strangers appear in her life uninvited, she becomes bewildered and disorientated.
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, leaving her wondering - just who is this strange woman at number 19 and why is Esther so obsessed with her?