Set in the sprawling metropolis of a grey London we meet Gina McVey (Lena Headey), a beautiful thirty something who works as a radiologist at a large hospital. At a surprise birthday party for her father we meet the people most important in her life: John (Richard Jenkins) is Gina’s dad and works for the American Embassy; her brother Daniel (Asier Newman), his girlfriend Kate (Michelle Duncan) and Gina’s boyfriend Steve (Melvil Poupaud). During the dinner party a mirror falls from the wall and smashes. The superstition of seven years bad luck creates a palpable tension in the air as they all clean up the debris.
The next day, on her way home, Gina sees herself drive past in her own car. Thrown, she follows the car and the woman up to her apartment, where Gina finds a photo of her father with her double. Shocked and bewildered, Gina flees the apartment and while driving away overshoots a red light and smashes into a truck.
Gina is brought home from the hospital by Steve and has difficulty remembering the details surrounding the crash. The complexity of what she thought happened, combined with a growing sense of dread, leads her to enlist the help of a counsellor, Robert (Ulrich Thomsen). Robert sets her on a trail to piece together the events before the accident and in doing so Gina starts to unravel a much deeper and darker secret that finally leads her back to her father. Together they go back to the beginning and to the apartment where she followed her double. Awaiting her there is a secret that will confirm her worst fears and change the boundaries of her reality forever.