LAPD SWAT officers Jack Traven and Harry Temple (played by Jeff Daniels) receive a distress call to respond to a precarious situation in a Los Angeles skyscraper. A deranged bomber (portrayed by Dennis Hopper) has taken an elevator full of hostages, threatening to release the emergency brakes and send them plunging to their doom unless a $3 million ransom is paid.
Displaying commendable quick thinking, Jack and Harry assess the bomb, devising a plan to use a cable from a window-washing crane to support the elevator. Unfortunately, the bomber outsmarts them, triggering the bomb, but miraculously, the crane holds the elevator long enough for the hostages to escape through an access panel. However, the tension escalates when they discover that the bomber has hidden himself in another freight elevator. Cornered, the bomber takes Harry hostage, forcing Jack to shoot Harry in the leg to secure his release.
Beaning the praise from Lieutenant "Mac" McMahon (played by Joe Morton) and with Harry receiving a promotion to detective, the duo believes they're done with danger. Unbeknownst to them, the bomber is still out there, lurking and watching the aftermath unfold on TV. The next day brings new horrors when Jack witnesses an explosion on a city transit bus that kills the driver. The bomber soon contacts Jack, revealing that another bus is rigged with explosives set to detonate once it drops below 50 miles per hour, while also demanding $3.7 million.
Jack desperately navigates the chaotic Los Angeles freeway, commandeering a civilian's car to get ahead of the speeding bus. He leaps onto the bus, where the dynamic quickly shifts as an onboard criminal accidentally injures the driver, Sam Silver (played by Hawthorne James). Panic ensues as passenger Annie Porter steps in to drive, and Jack must reveal the bomb to calm the frayed nerves of the frightened passengers. As he examines the deadly device, he enlists Harry's assistance in identifying their adversary.
Despite chaotic events that culminate with a bomb detonation claiming the life of a passenger, Jack encourages Annie to maintain their speed to tackle an incomplete freeway gap. They barely succeed and head toward Los Angeles International Airport for safety. Meanwhile, Harry tracks down the bomber just to find that he is a former police officer named Howard Payne, who manages to outsmart them by rigging his home to explode, resulting in the tragic loss of Harry and his team.
At the airport, Jack receives permission to speak to Payne, insisting he needs to discuss the ransom face-to-face. Though the press's presence is neutralized in the controlled airspace, Jack continues to worry that the bomber will somehow remain aware of their maneuvers. In a tense sequence, Jack attempts to disarm the bomb beneath the bus, but after a series of mishaps and the realization of Harry's death, Jack finds himself racing against time.
In a sharp twist of fate, Payne tricks Jack into believing he will rescue Annie, but he has instead sent her on a deadly mission. The dramatic chase unfolds as Jack follows Annie into a subway system, not realizing she’s fitted with an explosive vest that Payne can detonate at will. With chaos spreading, Payne commandeers a subway train, unleashing mayhem as Jack stealthily boards the train, ready to face off against this demented adversary.
In a gripping and climactic battle atop the train, Jack manages to defeat Payne in a dramatic showdown, ultimately freeing Annie from her shackles. Jack then pushes the train to its limits, causing it to derail spectacularly onto Hollywood Boulevard. In the end, Jack and Annie share a triumphant kiss, while the crowd around them gasps in disbelief at their daring escape from certain death.
