Rosy is the responsible sister. Amy is the free spirit, always breaking the rules.

But between them lies a secret; one they've sworn to keep safe, whatever the cost. When Amy confides in James, her new psychiatrist, he begins to suspect one sister is covering for the other. Instinct tells him to run, but his own dark past draws him ever closer to the two women, and they to him.

As cracks form in the sisters' facade, something becomes clear: three's a crowd, and one of them has to go.