Lydia Masters is a well-to-do mother and housewife who lives in a large estate set in a rainforest of northern Queensland. Her estranged identical twin sister, Janine, arrives on her doorstep. Shortly thereafter Lydia’s father-in-law, living in Texas has a stroke and her husbande Clay, must leave Lydia alone to deal with her bitter sister.

Janine harborsa jealousy toward Lydia born from her father’s treatment of her in the past. She tries to address this skewed past, but Lydia denies their father gave her preferred treatment and tells Janine to take responsibility for her failures. Janine sees the way Lydia follows  in her father’s footsteps with her children and it brings her satisfaction to see the same pattern at play.

Janine begins to commit acts which convince the family she is becoming violent, at the same time drugs Lydia, pushing her toward a breakdown. Lydia attempts to fight back while Janine convinces the housekeeper it is Janine who needs to be locked away.

Janine pushes Lydia too far and a physical fight, engineered by her, erupts between them. Lydia is knockedout  and Janine locks her in a bedroom. The police are called and are mis-informed, leading to  Lydia being admitted to a hospital under Janine’s name.  She is sent away to a private mental facility with no prospect of convincing anyone of her victimhood.  

Janine lives with Clay pretending to be his wife while Lydia fights for her sanity in the institution. Lydia begins to understand her lack of empathy is whatcaused  this but cannot persuade the incompetent psychiatrist to believe she is Lydia Masters.

Lydia pretends to take the drugs they administer to her and gradually regains her senses.  She embraces Janine’s identity in therapy and faces the pain she has caused her sister. She is pronounced ‘cured’ and released. She returns home to make amends with Janine, but her poor sister has cracked and believes she really is Clays’ wife and a violent confrontation unfolds. A shootingtakes  place and Lydia almost succumbs to her injuries but survives, a kidnapping occurs, and in the end Janine is locked up in the same mental facility. Lydia makes sure her sister is cared for so she can get on with her life.