When Heidi Banning learns that her estranged brother Henry has committed suicide, she is deeply saddened...but not shocked. Henry's mental illness is what drove them apart years ago, when he abruptly declared Heidi to be an imposter.

Haunted by the memory and desperate for closure, Heidi travels to Henry's desert home to pack his belongings and prepare the property for sale. There she meets and befriends Tina and Tracy, identical twins living next door, who regarded Henry as a friend and share in Heidi's grief.

But all is not as it seems. Heidi comes across evidence suggesting Henry had become obsessed with the twins' mother Natalie, a flaky alcoholic with a dangerous boyfriend... When Heidi seeks answers, she unearths a surreal tangle of lies, violence and — most disturbingly — impostors. The truth Heidi uncovers is in fact so bizarre that her grip on reality is called into question.

But is Heidi really losing her mind? And why are the twins suddenly taking such a keen interest in Heidi's personal life? What are they really after, and what might they be capable of in order to get it?

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the dual is an intense psychological thriller that explores the nature of identity, instinct, and innocence — and what we will do in order to survive.