The film opens with a scene of a raptor being put into the Jurassic Park facility while in a cage, but the raptor is able to catch one of the handlers and kill him while the others attempt to electrocute it. We then learn that John Hammond has created Jurassic Park, a theme park with bioengineered dinosaurs created on Isla Nublar off the coast of Costa Rica. He has invited Dr. Alan Grant and his partner/love Dr. Ellie Sattler along with mathematician and chaos theorist Ian Malcolm to the park.
Hammond takes them all on a tour of the facilities, giving them a theme park tour which explains in general terms how they bioengineering dinosaurs using the blood from fossilized mosquitoes and combined it with DNA from frogs to fill in the gaps of the missing links for completing the DNA. The dinosaurs were all created to be females so that there can't be any breeding. Malcolm upon learning of the this immediately knows that this is not good, that only something bad will come of it as genetic engineering has never proven to yield positive results.
Then, Hammond then brings his grandchildren Lex and Tim to join the group on a guided tour of the park in jeeps, but Hammond stays behind to oversee the park from the control room. Most of the dinosaurs they are seeking to experience aren't seen though during the tour and a tropical storm begins to threaten the island. This causes most of the employees to leave the island via boats to the mainland.
We then learn that Dennis Nedry feels undervalued by Hammond and has decided to steal embryos from the park which he has sold to Hammond's corporate competitor for a large sum of money. Nedry has programmed the Park's computer system to start a virus in order to allow him to leave the island untraced, but it also shuts down the electric fence which keeps the dinosaurs enclosed. Nedry is then killed by a venom spitting dinosaur before he can exit the park and the embryos he was sneaking out are lost.
Tim, Lex, and Grant, Malcolm, and Ellie are all stuck in the electrically run jeeps as Nedry's computer virus has been run and the rain begins to pour down. Soon after a Tyrannosaurus Rex begins to test the fence and discovers it no longer is electrically charged and breaks through. Lex attempts to get a flashlight which the T Rex sees and when Tim closes a door on the jeep the T Rex begins to topple the jeep with the kids inside. The kids are able to escape as Grant and eventually Malcolm lead the beast away.
Grant, Lex and Tim are split off from the group after this and must take refuge in the large trees to rest after the jeep they were in fell into a tree on the dinosaurs side of the fence. Here they find the shell of dinosaur eggs which reveals that the dinosaurs have been breeding when they were not supposed to be capable of doing so.
Hammond is back at the control center with chief engineer Ray Arnold who tells Hammond they have to reboot the entire system in order to bypass Nedry's virus. But Arnold has to go to a maintenance shed across the park to reboot everything and never returns as he is killed in doing so. By this point all of the electric fences have been shut down and the raptors have gotten free, and they kill Muldoon, the game warden of the Park but Ellie is able to get into the maintenance shed to get the power back on before the raptors get to her.
Grant, Lex and Tim reach the visitor center and Grant assumes they are safe and leaves the kids to look for Ellie. But the raptors are still on the loose and come after the children in the kitchen of the visitors center. The power if finally fully restored but the group once they are rejoined together is cornered by the raptors. When all seems hopeless the T Rex bursts through the visitor center and kills the raptors and the group is able to escape into Hammond's jeep and are led off into a helicopter off the island.
