Four months before Christmas, Sarah and Matthieu Scarangelo were in a car crash, of which Sarah and her unborn baby were the only survivors. On Christmas Eve, Sarah stays home alone, where she grieves her husband and prepares to go to the hospital the next morning for the delivery. As night falls, a woman knocks on Sarah's door asking to use the phone. When she refuses, the woman reveals that she knows Sarah and tries to force her way in. Sarah calls the police; they inspect the home and determine the woman has left, but promise to keep watch over Sarah through the night. The woman returns and tries to take Sarah's unborn child, but Sarah locks herself in the bathroom. The strange woman torments Sarah through the night and kills all who try help her.
While driving in a rainy day, the pregnant photographer Sarah crashes her car against another one in a road with no survivors. Four months later, in Christmas Eve, Sarah decides to stay alone at her home, grieving her deceased boyfriend Matthieu and preparing to go to the hospital on the next morning for the delivery. During the night, a stranger wearing black heavily hits on her front door asking to get inside, but Sarah calls the police and the woman vanishes. Later, while sleeping, Sarah is attacked by the woman that broke in her house with a pair of scissors and she runs to the bathroom. During the bloody night of terror, the woman attacks Sarah's visitors and discloses to Sarah who she is and what she wants.
Depressed and gloomy after the ghastly car accident that killed her husband in a head-on collision, mother-to-be Sarah is suddenly left all alone. Four months later, with Christmas Eve just around the corner, nothing much seems to have changed in Sarah's mental condition; she is still unable to come to terms with her loss, she is overcome with silent grief, finding refuge only in her work as a photojournalist. And then, unexpectedly, in the middle of the night, a knock on her door by an obscure woman in distress will be the beginning of a demented razor-sharp nightmare, as the unrelenting raven-haired intruder has deeply malevolent intentions. Is there a way out of this horror?
Four months after the death of her husband, a woman on the brink of motherhood is tormented in her home by a strange woman who wants her unborn baby.
- The film opens with a shot of a baby in utero with the mother's voice soothing it. The baby recoils as if struck. Expectant mother Sarah (Alysson Paradis) has been in a car accident, and her husband has been killed. Months later on Christmas Eve, Sarah is making final preparations for her delivery the following day. In light of her husband's death, Sarah is now moody and depressed.
That evening, a mysterious woman (Béatrice Dalle) arrives at Sarah's door asking to use the telephone to call for help. Suspicious, Sarah lies that her husband is sleeping and she does not want to be disturbed, but the woman tells her that she knows that he is dead. When the visitor persists on coming in, Sarah, a professional photographer, attempts to take her photo through a window and telephones the police. When they arrive, the woman has already vanished. The police assure Sarah that she will be fine, but arrange to have a patrol car visit throughout the night.
Upon developing her photos, Sarah recognizes the woman in the background of an earlier photo that Sarah had taken, indicating she was stalking Sarah over the past several days. Sarah telephones her employer, asking to have the photos enhanced.
As Sarah goes to bed, the woman sneaks into her house and arrives in the bedroom, awakening Sarah with scissors puncturing her navel. Sarah fights the visitor off and locks herself in the bathroom, where the woman tries to gain entry. The woman makes clear that her intentions are to take Sarah's unborn child for herself.
Sarah's employer arrives, and later her mother, both unaware of the predicament that Sarah is in. Believing her to be the attacker, Sarah accidentally kills her mother. Her employer is later stabbed to death by the mysterious woman. A little later, two policemen arrive to check up on Sarah, and upon realizing what is going on, attempt to apprehend Sarah's assailant but they are also murdered by the mysterious woman.
A final confrontation ensues between Sarah and the woman, with both of them injuring each other via various household appliances. Sarah manages to gain the upper hand on her attacker and burns off half the woman's face with an aerosol container and a lighted cigarette that the woman smokes. The severly burned woman flees, and upon being cornered by Sarah in the living room, reveals her identity; she was the other driver in Sarah's car accident and, being pregnant at the time, had suffered a miscarriage and lost her child. (Thus, the baby in utero at the beginning and the mother's voice at the beginning of the film was not Sarah's at all, but rather the woman's.)
The two are interrupted by the revival of one of the police officers; having been shot in close proximity by the woman with his riot gun, he survived the attack and was brain-damaged instead. In his current state of mind, he confuses Sarah with her attacker and brutally beats her with his club. The woman comes to Sarah's aid and kills the officer, but it is too late; Sarah has begun to give birth and the baby is stuck. Desperate to save the child, the woman proceeds to perform an impromptu Caesarian section on Sarah with her scissors.
In the final scene, Sarah lies dead on the stairs drenched in blood while the murderous deranged woman, having been successful with her delivery, sits on a rocking chair and comforts the newborn child.