Wealthy businessman John Hammond has created an animal theme park called Jurassic Park, featuring cloned dinosaurs and prehistoric plants, on the Costa Rican island of Isla Nublar. Following an accident at the site in which a worker is killed, lawyer Donald Gennaro, representing Hammond's investors, insists that he gets experts to certify his park is safe.
Hammond takes a group consisting of Gennaro, mathematician and chaos theorist Ian Malcolm, paleontologist Dr. Alan Grant and paleobotanist Dr. Ellie Sattler, to see the park. They are shocked to see living dinosaurs, including Brachiosaurus, upon arriving. Hammond reveals that the dinosaurs were created by a team of genetic scientists through cloning, a process that uses preserved ancient DNA from mosquitoes that are found inside amber, with DNA from frogs being used to fill in missing genomes. Chief geneticist Dr. Henry Wu points out that breeding is prevented by having all dinosaurs genetically engineered as females, but Malcolm theorizes that nature will overcome this obstacle in time.
Hammond arranges for the group, joined by his grandchildren Tim and Lex, to take a tour of the island in electric vehicles, while he oversees the tour from the control room with computer worker Ray Arnold and lead computer programmer Dennis Nedry. The group encounters a sick Triceratops during the tour, but other dinosaurs fail to appear, and the tour is cut short when a tropical storm approaches the island. Sattler stays behind with the park's veterinarian to study the Triceratops, while the rest of the group heads back to the visitor center.
Nedry had earlier been approached by Dodgson, a representative of a rival corporation, to steal dinosaur embryos for them. With most of the park's employees leaving for the mainland, Nedry shuts down the park's security systems to gain access to the embryos and the island's dock, where he will drop off the embryos. Nedry's sabotage also cuts power to the tour vehicles, stranding them in front of the Tyrannosaurus rex paddock as the storm hits. The Tyrannosaurus escapes the paddock and attacks the vehicles, devouring Gennaro, injuring Malcolm, and forcing Grant, Tim and Lex into the park's dinosaur reserves. Sattler, joining the park's game warden Robert Muldoon, attempts to rescue them, but they are only able to find Malcolm and must retreat with him when the Tyrannosaurus briefly pursues them. Nedry, having acquired the embryos, attempts to reach the dock, but loses his way in the storm, becomes stranded, and is killed by a Dilophosaurus.
The storm passes, and the following morning, Grant and the children come across broken egg shells. Grant deduces that the dinosaurs were given the DNA of west African frogs, who can change from male to female in a single-sex environment, thus proving Malcolm right that breeding control methods would fail. The trio proceeds to return to the visitor center.
