En 1944, alors que la guerre du Pacifique fait rage, deux pilotes s'écrasent sur une île inconnue. L'un est Américain, l'autre est Japonais. Alors qu'ils s'affrontent sur place, ils sont brusquement interrompus par une gigantesque créature...
In 1933, at the height of the Great Depression, New York City vaudeville actress Ann Darrow has lost her job and is hired by financially troubled filmmaker Carl Denham to star in his new film. Ann signs on when she learns her favorite playwright, Jack Driscoll, is the screenwriter. As their tramp steamer, the SS Venture, makes the lengthy journey to the remote and mysterious Skull Island, Ann and Jack fall in love. Captain Englehorn begins having second thoughts about the voyage, prompted by crew speculation of trouble ahead.
In 1954, a nuclear bomb is detonated at the moment a giant creature emerges from the ocean. In 1999, Project Monarch scientists Ishiro Serizawa and Vivienne Graham investigate a colossal skeleton unearthed in a collapsed mine in the Philippines. They find two spores; one dormant and one hatched that made a trail into the sea. In Japan, the Janjira Nuclear Power Plant experiences unusual seismic activity and Supervisor Joe Brody sends his wife Sandra and a team of technicians into the reactor. A tremor breaches the reactor, leaving Sandra and her team unable to escape while the plant collapses.
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.
In 2013, Earth's coastal cities come under attack from Kaijus, colossal beasts that periodically emerge from a dimensional portal on the Pacific Ocean floor called "The Breach." To fight them, the Pacific Rim nations build the Jaegers, equally colossal humanoid war machines. Each Jaeger is controlled by two or more pilots whose brains are linked, called "drifting" to share the heavy mental load of operating the machine. The Jaegers are initially effective, but many are destroyed as the Kaijus grow more powerful and their attacks become more frequent. In 2025, the participating governments deem the Jaeger program unsustainable and discontinue it in favor of building defensive coastal walls. The four remaining Jaegers are redeployed to Hong Kong to protect the coast until the walls are completed. Jaeger commander Stacker Pentecost resolves to make a last-ditch attempt to end the Kaiju threat by destroying The Breach with a nuclear weapon, even though past nuclear strikes on the portal have been unsuccessful.
On the day of her wedding to news weatherman Derek Dietl, Susan Murphy is struck by a meteorite and its energy causes her to suddenly grow over fifty feet in height during the ceremony. She is tranquilized and awakens in a top secret government facility that houses monsters without human knowledge. She meets the warden W.R. Monger, and fellow inmates: Dr. Cockroach P.H.D., a mad scientist who became half cockroach after an experiment; B.O.B. (Benzoate Ostylezene Bicarbonate), a brainless, living mass of goo as a result of a food flavoring mutation; Insectosaurus, a mutated bug standing at over 300 feet in height, and The Missing Link, a prehistoric fish man who was thawed from deep ice; and Susan herself has been renamed to Ginormica. Meanwhile, in deep space, an alien named Gallaxhar is alerted to the presence of quantonium; a powerful energy source on Earth, and he sends a probe to retrieve it. After the probe crash lands on Earth, the president attempts to make first contact with it by playing a keyboard version of Axel F, but it begins to rampage toward San Francisco.
Following a nuclear test in French Polynesia, the fallout irradiates a lizard's nest. Decades later, an enormous sea creature suddenly attacks a Japanese fishing vessel in the South Pacific, leaving only one fisherman alive. Dr. Niko "Nick" Tatopoulos, an NRC biologist, is sent to Tahiti and to Jamaica, where a wrecked village, footprints, and ship are found. Nick collects skin samples that lead him to believe the creature is an enormous mutant created by nuclear testing. It travels to New York City during the rainiest week of the season, leaving a path of destruction in its wake.
Dix ans après la fermeture de la brèche, le monde se reconstruit et vit désormais en paix sans les Kaijûs. Jake, fils du célèbre Marshall Stacker Pentecost (mort en héros), vit de vols et de troc tout en fuyant le passé familial. Il va faire la connaissance de la jeune Amara Namani, qui a fabriqué son propre Jaeger (les robots géants qui ont permis d'affronter les monstres). Ils sont tous deux arrêtés pour vol de matériel de Jaeger et construction illégale de Jaeger, et afin d'éviter la prison, sont obligés d'accepter d'être embarqués sur une base militaire en Chine où Jake retrouve son ancien copilote de jaeger, Nate Lambert, afin de former les nouvelles recrues pilotes, qu'Amara rejoint. Sur place, tout le monde est en effervescence car les Jaegers sont sur le point d'être rendus obsolètes par le vote d'un programme de drones produits par Shao Corporation et développés par Liwen Shao et le Dr. Newt Geiszler. Jake retrouve par ailleurs sa demi-sœur, Mako Mori, devenue Secrétaire Générale du Pan Pacific Defense Corps. Mais alors que le sommet pour le vote est sur le point de commencer à Sydney (QG du PPDC), un Jaeger illégal débarque et attaque la ville, tuant Mako Mori.
In the Kingdom of Cloister, Jack, a young farm boy, is fascinated by the legend of Erik, an ancient king who defeated an army of invading giants from a realm in the sky by controlling them with a magical crown. At the same time, Princess Isabelle becomes fascinated with the same legend.
The film is presented as found footage from a personal video camera recovered by the United States Department of Defense. A disclaimer text states that the footage is of a case designated "Cloverfield" and was found in area US447 "formerly known as Central Park". The video consists primarily of segments taped the night of Friday, May 22, 2009. Occasionally, older segments are shown from a previous video that was mostly taped over.
In the 23rd century, Earth has become a space-faring federation. While colonizing new planets, humans have encountered an insectoid species known as Arachnids or "Bugs", with their home being the distant world Klendathu. The bugs appear to be little more than killing machines, though there are suggestions that they were provoked by the intrusion of humans into their habitats.
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.
In late 2000, an American military pathologist commands a reluctant Korean assistant to violate protocol by dumping over 200 bottles of formaldehyde down a drain leading into the Han River. Over the next few years, there are sightings of a strange amphibious creature in the waterway, and the fish in the Han River are dying off because of water pollution. A suicidal businessman, just before jumping off a bridge into the river, sees something dark moving under the surface of the water.
Shortly after the dawn of the new millennium, during construction on the London Underground, workers penetrate an underground cave. A huge dragon emerges from hibernation, incinerating the workers with its flaming breath. The only survivor is a boy, Quinn Abercromby (Ben Thornton), whose mother Karen (Alice Krige) is the construction crew chief; Karen is crushed to death while protecting Quinn as the dragon climbs to the surface. It flies out of the Underground and more dragons appear, multiplying rapidly. Shown in newspaper clippings and a voiceover, scientists discover that dragons are a lost species responsible for the extinction of the dinosaurs by incinerating them and eating their ash, as well as ice ages. The dragons are speculated to hibernate after destroying most of the Earth's creatures until the planet repopulates. After the dragons' awakening humanity resists militarily, including a 2010 use of nuclear weapons; this, however, hastens the destruction and within a few years humans are nearly extinct.