Jess picks up his girlfriend, Nicole, in his convertible to head out to California. On the way, Nicole complains she needs to pee and after refusing to go on the side of the road, urges Jess to find a rest stop, which he finds almost immediately. Nicole enters the women's restroom and finds terribly messy and dirty conditions. She then exits the building to find her boyfriend gone. She calls out for him many times, and after receiving no reply, she is convinced he is gone. Her thoughts are reinforced when the deranged truck driver with license plate KZL-303 throws her the red cell phone that was in the convertible. Nicole goes to look for help and notices an RV and bangs on the door and asks for help. She has a short eerie ride with the passengers until she is eventually thrown out for looking at the deformed individual hidden behind curtains at the back of the vehicle.
She then returns to the restroom. Nicole hears a girl coughing up blood with cuts all over whimpering in the maintenance room. She cautions Nicole about the deranged killer who tortured her. Then the girl bleeds profusely and as Nicole's attention is diverted she disappears, blood and all.
The man in the yellow truck continues to elude Nicole, until a cop arrives via motorcycle. At this point she feels saved, happy to have help arrived. Her happiness is temporary however, as the cop soon falls victim to the driver of the yellow truck by being completely oblivious to the situation and allowing the driver of the yellow truck to rev his engine and run him over without as much as an attempt to evade it. Then the officer's legs are run over repeatedly and injured severely in the process.
Nicole is able to drag the officer to the rest room, where the two seek refuge from the psychopath. The cop eventually realizes that the situation they are in is hopeless. He tries to calm Nicole down, and tells her about his family. Eventually, the driver of the truck returns and locks Nicole and the officer in the restroom. Nicole, thinking the man has left, attempts to open the lock. The driver appears out of seemingly nowhere, and bites Nicole's finger off. The officer realizes that Nicole is going into shock and commands Nicole to shoot the driver when he returns. She fires four shots out of the officer's revolver into the door but is unable to see if she has struck the driver. The driver then drops a camera into the restroom via the open window. The video is of Jess being tortured with a knife; Jess then says he loves Nicole. The last shot of Jess shows him having his tongue cut out. The driver feeds a hose through the window and starts pouring gasoline into the room. Nicole tries to find an escape and is able to open a hatch in the ceiling. Realizing there is no way for her to get him out of the building the officer tells Nicole to use the two remaining bullets in his gun to kill him because he would rather die that way than be burned alive. She fails at first but eventually succeeds in the grisly task. The driver lights the gasoline and Nicole hurries to get out of the building. As Nicole is escaping she notices that the officer's body has mysteriously disappeared. Nicole is able to jump from the roof before the building explodes.
Once she is on the ground again, Nicole encounters the man in the yellow truck once again. He exits the truck, and she sneaks up behind him, striking him with a tire iron. She turns him over and is shocked to discover it is actually Jess, with his mouth sewn shut, sporting other visible wounds.
Nicole sneaks to the convertible where she fills a whiskey bottle that she had retrieved from a nearby Park Ranger's station full of gasoline, in order to concoct a makeshift Molotov cocktail in order to use against her attacker should he return.
Morning approaches, and she walks down the highway, with the driver of the truck approaching her at a rapid speed. After some fumbling, she is able to strike a match and light her Molotov cocktail. She hurls the bottle at the truck and almost instantly it is consumed by flames, followed by a large explosion. After a few moments, the camera view changes to behind Nicole. She starts to run away, but as soon as she turned, a man looking very much like Jess is right there, and she and everything then fades to black.
As an epilogue, the film ends with a totally different girl going to the same rest stop, after it is renovated after the fire. She discovers Nicole in the maintenance room, and runs out to the Park Ranger (who has returned to his post) to inform him of her discovery. He goes into the room, after unlocking it, and no one seems to be present. After he leaves, Nicole is shown behind some janitorial equipment calling out for help and vomiting blood.
The next scene is from the view of a video camera. It shows the father from the RV burying the body of the man in the truck. the man realizes he is being taped, and goes into the RV and tells his deformed son that "This is our little secret."
The last scene shows the yellow truck driving down a deserted road.