A baby in utero is seen, with the mother's voice heard soothing it. The baby recoils as if struck. Expectant mother Sarah (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. Still reeling from her husband's death, Sarah is now moody and depressed.
That evening, a mysterious woman (Dalle) arrives at Sarah's door, asking to use the telephone to call for help. 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 she had taken, indicating she was stalking Sarah. Sarah telephones her employer, asking to have the photos enhanced. As she goes to bed, the woman arrives in the bedroom, awakening Sarah with scissors puncturing her pregnant belly. 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 child for herself.
Sarah's employer arrives, and not knowing what Sarah's mother looks like, takes the strange woman's word that she is the mother. Later her actual mother arrives, arousing the employer's suspicion. Believing her to be the attacker, Sarah accidentally kills her mother by stabbing a needle into her mother's neck. Her employer is later stabbed to death by the mysterious woman. The police arrive to check up as promised earlier. Not knowing what Sarah looks like, the police take the mysterious woman's word that she is Sarah and everything is fine. Just as they are about to leave, the police realize the woman who answered the door was not pregnant. They enter the home but are all eventually brutally murdered by the attacker. The first is stabbed to death with knitting needles as he attempts to arrest the attacker. The second is shot in the back of the head as he attempts to help Sarah. The third, along with his prisoner, is killed after the attacker kills the power.
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 cigarette. The woman flees, and upon being cornered by Sarah, reveals her identity; she was the other driver in Sarah's car accident and, being pregnant at the time, had lost her child.
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 but was disoriented and blinded. In his current state of mind, he confuses Sarah with her attacker and brutally beats her in the stomach 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 the impromptu Caesarean section on Sarah with her scissors as she originally planned. With Sarah lying dead on the stairs, drenched in blood, the woman, having been successful with her delivery, sits on a rocking chair and comforts the newborn child.Béatrice Dalle as La Femme
Alysson Paradis as Sarah Scarangelo
Nathalie Roussel as Louise Scarangelo, Sarah's mother
François-Régis Marchasson as Jean-Pierre Montalban
Jean-Baptiste Tabourin as Matthieu
Dominique Frot as The Nurse
Claude Lulé as The Doctor
Hyam Zaytoun as Policewoman
Tahar Rahim as Policeman #1
Emmanuel Guez as Policeman #2
Ludovic Berthillot as BAC Policeman #1
Emmanuel Lanzi as BAC Policeman #2
Nicolas Duvauchelle as BAC Policeman #3
Aymen Saïdi as Abdel Shani Essadi
Julien Maury and Alexandre Bustillo met each other through a mutual friend. After the meeting, Bustillo sent Maury a first draft of the script and Maury sent over some short films that he had worked on in the past. According to Maury, "The first idea with the story was to change the sex of the killer. In horror movies it’s always a guy chasing after young girls; it’s one of the clichés of the genre. So the first main idea was changing the identity of the bad guy. We wondered what was the motivation for a woman to hunt another woman?" The film was given a budget of 1.7 million Euros.
Inside received mostly positive reviews. Rotten Tomatoes reported that 83% of critics gave it a positive review.
Bloody Disgusting ranked the film twelfth in their list of the 'Top 20 Horror Films of the Decade', with the article saying "One of the most audacious, brutal, unrelenting horror films ever made, Inside is perhaps the crown jewel of the new wave of extreme French horror films."
The DVD label Dimension Extreme picked it up for a US release in 2008. The movie has been released on Blu-ray in Sweden and Taiwan.
Hollywood has shown interest in remaking the film; Maury and Bustillo were propositioned but both turned it down.
Jaume Balagueró, the director of REC, told Fangoria that he may be directing the remake in the future and that it would "accent the terror of the pregnancy situation more than the gore".
Recently, Maury mentioned that there had been some problems with the rights and the project was delayed. Furthermore, he was unsure if Balagueró’s was still attached to the project; "For us this was really like a dream because we are big fans of Balagueró’s movies. For the first time it wasn’t the case of a newbie making the movie of a big director, it was the exact opposite where a huge director is making the film of two poor French guys. So we were proud of that."
In 2015, it was announced that the remake was back in production. Miguel Vivas, known for directing Kidnapped, is set to direct.