In Los Angeles, California, an elevator full of people is held hostage by a bomber, Howard Payne, who demands $3 million from the Los Angeles Police Department (LAPD). Payne is outwitted by two LAPD SWAT team members, Jack Traven and Harry Temple. He attempts to flee by detonating a bomb that appears to kill him. However, sometime later, the mastermind re-emerges with a new ransom plot. After blowing up a Los Angeles city bus, Payne calls Jack Traven via payphone to warn that a second bus has been rigged with a similar bomb. Once that bus reaches fifty miles-per-hour, the explosive will arm, at which point the bus cannot dip below that speed or the bomb will detonate. Payne demands $3.7 million to deactivate the bomb, and warns that in the meantime, all passengers must remain on the bus. Jack manages to board the bus just before one of the passengers, a paranoid criminal, panics and shoots the driver, Sam. To keep the bus moving at the designated speed, passenger Annie Porter takes the injured driver’s seat. She and Jack work together to maneuver the bus to the airport, going so far as to jump the vehicle over a fifty-foot gap on an elevated freeway under construction. Once they reach the airport, Jack negotiates with Payne to allow Sam, the injured driver, off the bus. However, when a passenger named Helen tries to escape as well, Payne detonates a smaller bomb that kills her. Jack’s superior, Police Captain McMahon, determines that Payne has been monitoring the situation inside the bus via a hidden camera. With the help of a local news crew, he carries out a plan to interrupt the camera feed, record a minute’s worth of footage, and place it on a loop. Thus, the bus is evacuated unbeknownst to Payne, shortly before it explodes. The bomber realizes he has been fooled just as police drop his ransom money in the designated spot. He takes the cash and, posing as a police officer, kidnaps Annie. Strapping a bomb-laden vest to her chest, he hijacks a subway train, and kills the conductor. Jack is in pursuit, however, and chases Payne onto the roof of the subway car, where Payne is decapitated by an overhead light signal. Jack defuses Annie’s bomb vest, but she remains handcuffed to a pole. Unable to free her, he speeds up the train to derail it onto a new track, still under construction. The two hold onto each other as the train jumps a curve onto the makeshift track. It skids upward, through the unfinished train station, onto Hollywood Boulevard. Jack and Annie kiss passionately as a crowd of onlookers gathers outside the wrecked train.