An unnamed man sneaks into Ocean View Amusement Park and plants a small radio-controlled bomb on the tracks of the park’s wooden roller coaster, The Rocket. The blast derails the train, injuring or killing riders, and safety inspector Harry Calder George Segal is called to investigate. A park worker recalls seeing a maintenance man on the tracks earlier in the day, but there’s no record of anyone being assigned there, hinting at a deliberate, organized crime behind the tragedy.
The bomber’s trail continues with a fire at a dark ride in Pittsburgh, and Calder begins to suspect a connection between the incidents. His fishing for links leads him to Chicago, where executives from the nation’s largest amusement-park chains are gathered for a meeting. Calder breaches the gathering and a tape from the bomber is played, revealing a demand for $1 million to halt the attacks.
Back home, FBI Agent Hoyt [Richard Widmark] arrives to explain the practical side of the case: the extortion money is to be delivered at Kings Dominion. Calder is ordered to wait at a public telephone there. The bomber phones in, warns that there’s a bomb in the park, and sends Calder a two-way radio to keep in contact. He directs Calder to ride several attractions, including the Rebel Yell roller coaster, and to use the radio as a means of control. While Calder rides the Skyway, the bomber reveals the bomb is hidden inside the radio and cautions him not to discard it, or it will explode on impact on the park’s crowded paths. He instructs Calder to feign a delivery and then leave the money on a bench. Calder complies, and later Hoyt admits he marked the money, violating the bomber’s instructions. Calder asks to be sent home and leaves the radio with the bomb squad.
The bomber returns with another threat, blaming Calder for the marked money and promising another attack. Calder, piecing together clues, deduces that the next target will be Revolution at Magic Mountain. Although the FBI initially resists his theory, they decide to investigate since the ride is set to debut on the Fourth of July, when crowds will surge. Agents disguised as park maintenance workers locate and disarm a bomb attached to the tracks.
The bomber then heads back to his car and secures a new bomb just as Revolution is about to open. To gain admission, he pays a guest $100 for a “Gold Ticket,” enabling him to be among the first passengers, and places the device under his seat in the rear of the train. After the inaugural ride, Calder recognizes the bomber’s voice during an on-site interview with a reporter and gives chase, warning the agents that something might be hidden in the coaster train.
The bomber is cornered and threatens to explode the ride, clutching the detonator as agents attempt to jam the signal. Calder accepts a firearm from an agent and begins to hand it to the bomber; the agents succeed in jamming the detonator, and Calder, in the process, accidentally shoots the bomber. He bolts, climbs onto the track, and, confronted by Calder, is struck and killed by the coaster train. In the aftermath, Revolution resumes operation once the danger has passed.
