While a group of teenagers are having an evening beach party on Amity Island, Chrissie Watkins (Susan Backlinie) goes skinny dipping in the ocean. Something violently grabs and pulls her underwater. In the morning, Deputy Hendricks (Jeffrey Kramer) finds her remains on the beach. Upon hearing from the medical examiner that the cause of death was a possible shark attack, Police Chief Martin Brody (Roy Scheider) proceeds to close the beaches, but Mayor Larry Vaughn (Murray Hamilton) overrules him, fearing news of a shark attack will ruin the summer tourist season, the town's primary revenue source. He rationalizes that there have been no prior shark problems in the area, and theorizes the girl was killed in a boating accident. The coroner concurs and Brody reluctantly accepts their conclusion.
Jonas Taylor est un ancien capitaine de la Marine et un plongeur spécialisé dans les eaux profondes. Il est recruté pour plonger dans l'océan Pacifique, pour sauver une équipe de scientifiques coincée dans l'épave d'un submersible attaqué et endommagé par un requin préhistorique de vingt mètres de long, connu sous le nom de Mégalodon. Engagé par un océanographe chinois, Taylor devra surmonter ses peurs et affronter une seconde fois le prédateur qu'il a auparavant rencontré lors d'une expédition pour sauver les hommes et les femmes piégés dans les profondeurs de l'océan.
Prior to a new hotel opening on Amity Island, a huge great white shark ambushes two divers who are photographing the wreck of the Orca, the late Quint's boat. A few days later, the shark devours a water skier. The speedboat driver defends herself by dumping gasoline on the shark (accidentally spilling some on herself) and shooting it with a flare gun, causing the boat to explode. The shark escapes but is severely scarred.
Charles Travis (Bruce Campbell) and Karen Ross (Laura Linney) are testing a communications laser in a remote part of the Congo near a dormant volcano when Charles' friend Jeffrey (Taylor Nichols) discovers an ancient lost city's ruins. When Jeffrey and Charles go to explore it, they are both mysteriously killed. While Karen waits at headquarters, she activates a video feed and sees a destroyed camp with several dead bodies. The camera is then suddenly knocked over by a strange creature, ending the transmission. TraviCom's CEO and Charles' father R.B. Travis (Joe Don Baker) reveals they were really exploring the Congo to find a rare blue diamond that's only found at the volcanic site.
Fred Wilson (Charles Grodin), an executive of the Petrox Oil Company, forms an expedition based on infrared imagery which reveals a previously undiscovered Indian Ocean island hidden by a permanent cloud bank. Wilson believes the island has a huge deposit of oil. Jack Prescott (Jeff Bridges), a primate paleontologist who wants to see the island for himself, stows away on the expedition's vessel. Prescott reveals himself when he warns the crew the cloud bank may be caused by an unknown beast. Wilson orders Prescott locked up, claiming that he is really a spy from a rival oil company. While escorted to lock-up, Prescott spots a life raft which carries the beautiful and unconscious Dwan (Jessica Lange). Wilson conducts a thorough background check on Prescott and realizes he is telling the truth. He appoints Prescott the expedition's official photographer and requests that he be present when Dwan revives because of his medical background. Upon waking, Dwan says she is an aspiring actress who was aboard a director's yacht which suddenly exploded.
A great white shark follows a team of water skiers. The driver stalls the ski boat but manages to restart it before the shark can approach. The shark follows the water skiers into the SeaWorld park and throws the gate off its rails while it is closing. Meanwhile, Florida announces the opening of SeaWorld's new glass covered underwater tunnels that allow close up views of the park's animals.
Fisherman Matt Boyd (Richard Dreyfuss) is fishing in Lake Victoria when a small earthquake hits, splitting the lake floor and causing a whirlpool. Boyd falls in, and is ripped apart by a shoal of piranhas that emerge from the chasm.
At Aquatica, a remote former submarine refueling facility converted into a laboratory, a team of scientists is searching for a cure for Alzheimer's disease. Fluids from the brain tissue of three Mako sharks are being harvested as a cure for Alzheimer's. Unknown to the other scientists, Dr. Susan McAlester (Saffron Burrows) has violated the code of ethics and has genetically engineered the sharks to increase their brain size, but this has the side effect of making the sharks smarter and more dangerous.
After witnessing gangster Eddie Kim brutally beat U.S. Prosecutor Daniel Hayes to death in Hawaii, Sean Jones is escorted by FBI agents Neville Flynn and John Sanders on a Boeing 747-400 to testify in a trial in Los Angeles. Despite increased security for the flight, Kim arranges for a time-release crate full of venomous snakes to be placed in the cargo hold in an attempt to bring down the plane before it reaches Los Angeles International Airport (LAX). To ensure the snakes attack the passengers without being provoked, he has one of his henchmen disguised as an airport ground employee spray the passengers' leis with a special pheromone which makes the snakes highly aggressive. The crate opens midway through the flight and the snakes make their way through the cabin. A couple having sex in the bathroom, and a man using the bathroom are the first killed. The plane's captain, Sam McKeon, investigates and fixes an electrical short, but is killed by the viper that caused it. Co-pilot Rick, unaware of the snake, believes Sam has suffered a heart attack and continues toward LAX.
Seth Brundle (Jeff Goldblum), a brilliant but eccentric scientist, meets Veronica Quaife (Geena Davis), a journalist for Particle magazine, at a meet-the-press event held by Bartok Science Industries, the company that provides funding for Brundle's work. Seth takes Veronica back to the warehouse that serves him as both home and laboratory, and shows her a project that will change the world: a set of "Telepods" that allows instantaneous teleportation of an object from one pod to another. Brundle convinces Veronica to keep the project's existence quiet in exchange for exclusive rights to the story, and she begins to document his work. Although the Telepods can transport inanimate objects, they do not work properly on living things, as is demonstrated when a live baboon is turned inside-out during an experiment.
In Aroostook County, Maine, marine Fish and Game officer Walt Lawson is attacked and bitten in half by something unseen in Black Lake. Sheriff Hank Keough (Brendan Gleeson), Fish and Game officer Jack Wells (Bill Pullman), American Museum of Natural History paleontologist Kelly Scott (Bridget Fonda), and mythology professor/crocodile enthusiast Hector Cyr (Oliver Platt) go to the lake to investigate.
Daniel Kintner (Daniel Travis) and Susan Watkins (Blanchard Ryan) are a couple frustrated that their hard-working lives do not allow them to spend much time together. They decide to head out on a scuba-diving vacation to help improve their relationship. On their second day, they join a group scuba dive. A head count is taken, and the passenger total is recorded as 20. Daniel and Susan decide to separate briefly from the group while underwater. Half an hour later, the group returns to the boat. Going by the tally sheet, the total comes to 20, though in reality, it is 18. Daniel and Susan are still underwater and have not yet realized that the others have returned. The boat leaves the site. Not long after, Daniel and Susan return to the surface and look for it. They believe the group will return to recover them in reasonable time.
Tracking two lost lumberjacks through the night, a rescue team nearly follows a hound over a cliff. Two men rappel down to retrieve the fallen hound, but they are killed. The third, hearing screams down below, rappels down to investigate, where he finds his team mates dead, only to be killed himself by an unseen entity.
Entomologist Dr. James Atherton (Julian Sands) searches the Amazon rainforest with the hope of discovering new species of insects and arachnids. Descending into an enormous sinkhole, his team sets up collectors on the ground below a large tree, then blow smoke up into the canopy of the tree. A large number of bugs fall into the collector, including a very aggressive new species of spider. The spider is captured and chloroformed for research; and is later revealed to be lacking sex organs, thus making it a drone, or soldier, highly unusual in an arachnid species. A nature photographer, Jerry Manley (Mark L. Taylor), who has been suffering a fever while traveling with the team, unknowingly has a fertile (non-drone) male spider of the same species jump into his backpack, that night sneaking into his sleeping bag and biting him. Manley has a massive seizure from the venom and dies. The remainder of the scientists takes his body back to the United States, blaming Manley's death on the preexisting fever. The spider crawls into the box and is sealed in with the corpse.