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.FINE
Output: Question: Who does Sarah accidentally kill?, Answer: Her mother