Before the premonition begins, the hydraulic pump beneath Lewis Romero's seat begins to leak when a roller coaster attendant secures his seat restraint.
The premonition begins when Wendy Christensen has sat herself toward the back of the roller coaster and pulls her digital camera out to snap a photo. The moment the camera takes the picture, a roller coaster attendant waves his hand in front of her, ruining the photo. He points to a sign explaining that no cameras or loose articles can remain on the ride. Kevin suggests that he put her camera in a pocket inside of his jacket. A few rows ahead, Frankie Cheeks overhears the attendant and conceals his video camera inside of his jacket. Kevin becomes excited for the ride until he withdraws his hand from the handlebar in front of him after getting his fingers stuck in sticky gum left by a previous passenger.
The attendants give the OK to start the ride, and the roller coaster begins its ascension to the top of the initial drop. As the ride progressses, the leaking hydraulic line rattles and loosens. While going through a loop, Frankie yells at Ashley Freund and Ashlyn Halperin to flash him. Annoyed, Ashlyn slaps the camera out of Frankie's hand, which magically catches onto and wraps around the tracks at the bottom of the loop. The coaster runs over the camera, which loosens a wheel on the left side of the front cart, and severs the hydraulic line and unlocks all of the safety restraints, threatening the lives of all of the passengers.
As the roller coaster continues along the tracks, the front left wheel pops off, showering sparks onto the passengers. The passengers scream in terror as they attempt to remain in their seats while the coaster runs through corkscrews, hills, and sharp turns. More pieces from the coaster train break off. As the coaster hops over a hill and makes a sharp turn, the force causes carts one through three to separate from carts four through six. The front three carts fly off the tracks, killing Carrie Dreyer, Jason Wise, Ashley, Ashlyn, Frankie, and five others.
Lewis is thrown out of his seat but manages to hang onto the coaster for dear life as it travels through more corkscrews. He loses his grip and is flung toward the back of the coaster where he is narrowly saved by Kevin Fischer. As Kevin catches Lewis, his seat restraint breaks away. Kevin manages to hang onto Lewis before a metal covering from the cart in which Lewis sat breaks away and smashes into him, sending him flying into a steel support beam, snapping his spine in half and causing a part of the support beam to jut out over a portion of the roller coaster tracks. The piece of metal that hit Lewis smashes onto another portion of the roller coaster tracks, causing the tracks to become uneven. The roller coaster continues to bunny hop toward another large loop, where, as it ascends toward the top of the loop, it begins to slow to a stop due to the train's missing wheel grinding against the tracks. The coaster becomes stuck upside down at the top of the loop. Erin Ulmer and Ian McKinley fall from their seats but are able to hang on to their restraints. Shortly after, they lose their grip, and Ian falls to his death, followed by Erin. Two unseen characters (later revealed to be Perry Malinowski and Julie Christensen) fall out of their seats to their deaths as well.
Kevin and Wendy attempt to get the coaster out of the loop by rocking it backward. They succeed, but in the process, Kevin gets his coat stuck on a broken piece of his missing seat restraint as the coaster goes backward. The piece of support beam that juts out over the tracks from when Lewis was killed slices through Kevin's torso, cutting him in half. Wendy screams in horror and cries before the coaster hits the dislodged portion of the track. The train scorpion-tails backward as it is ripped off from the tracks and falls to the ground. Wendy is thrown out of her seat as the coaster falls, and she is killed when she lands on another portion of tracks below.
It is then revealed that the derailment was a vision of Wendy's, and the roller coaster is still at its station. She panics and the roller coaster attendants release the seat restraints only in carts four through six, allowing several of the students off before a large fight ensues. Ashley and Ashlyn get off the ride, followed by Frankie who is videotaping them. Jason attempts to leave the coaster, but can't get the attention of the ride operator due to the fight. The remaining passengers begin to chant "Hey! Ho! Let's go!", prompting the ride operator to start the ride.
As a security guard leads Wendy and the other students toward the exit of the ride, Wendy notices Jason is still in the roller coaster. Panicked, she runs back to the ride platform and tells the attendants to stop the ride, but is forced outside of the ride exit. As Wendy and Kevin are escorted away from the ride, the roller coaster crashes, killing Jason, Carrie and five others.