High Tension

Haute Tension (High Tension, also known as Switchblade Romance in the UK) is a 2003 French horror film directed by Alexandre Aja and staring Cécile de France, Maïwenn Le Besco and Philippe Nahon.

Marie (de France) and Alex (Besco), are two college students and longtime friends on their way to stay at Alex's parent's house for the weekend so they can study in peace. In the night, however, an insane truck driving Serial Killer (Nahon) comes to the house and murders Alex's family. He then abducts Alex herself. Marie goes after her with the intention of rescuing her, but it turns out the killer is not who he seems...

Critical reception was mixed to negative, with criticism generally being directed at the twist ending which, inasmuch as it might make M. Night Shyamalan proud, also generates a gaping Plot Hole.

The original version was rated NC-17, and some bits had to be cut for it to be rated R.

Tropes used in High Tension include:

Chainsaw Good: Both the killer and Marie get a turn with a circular saw.
A Date with Rosie Palms: Marie, after seeing Alex showering through the bathroom window earlier that night. Since she's listening to her walk-man during the act, this prevents her from hearing the killer get into the house until the murders are well under way.
Final Girl: Subverted, in that the protagonist is also the killer, leaving both Alex and the killer alive in the end.
Foreshadowing: There is a lot of this, thought most is nigh impossible to register without knowing the Plot Twist... and some even then.
Girl with Psycho Weapon: During the film Marie is depicted weilding both a wooden club wrapped in barbed wire (as shown above) and a circular saw.
Gorn
Gory Discretion Shot: While Alex's parents are shown to be brutally killed on screen, the audience only sees a glimpse of gunfire when the killer shoots Alex's kid brother in a corn field.
Hey It's That Girl: Though you probably won't recognize her, Maïwenn Le Besco was the Diva in The Fifth Element.
The Killer in Me
A Love to Dismember: Near the start of the film, the killer fellates himself with a woman's severed head.
Madness Mantra

"I won't let anyone come between us anymore, I won't let anyone come between us anymore..."

Psycho Lesbian
Serial Killer
Slasher Movie: A strange example, as it seems to almost turn into an action movie at around the midpoint.
Twist Ending: The killer is in fact Marie; the truck driver is an alternate personality whom her normal side perceives as a seperate being, à la Fight Club. Marie had a lesbian crush on Alex, and her alternate personality murdered her family so nobody could come between them though she, believing the alternate personality to be a different person, would not have to feel any guilt.
- It's worth noting that this twist is unique to the movie, although the original novel by Dean Koontz isn't that well known anyways.
Unreliable Narrator
Visual Pun: Both of Marie's personalities came at the same time.
Yandere: The killer wants Alex all to herself, and is not opposed to brutally murdering her entire family to do it.
- And everyone that comes across afterwards. Unfortunate drivers on forest roads beware.