Chuck Levine, a womanizing bachelor, and Larry Valentine, a widower struggling to raise his two children, are two veteran New York City fire fighters. During a routine sweep of a burned building, a segment of floor collapses on Chuck. However, Larry quickly shields him from the falling debris, saving his life. Later, he and Chuck wake up in a hospital, where Chuck vows to repay Larry in any way possible. This incident serves as a catalyst for Larry's epiphany: death is both inevitable and unpredictable. This prompts him to significantly increase his life insurance policy, but he runs into difficulties naming his children as primary beneficiaries in his policy. He is told he should get remarried so his new spouse could be the primary beneficiary; however, it doesn't specify who he has to marry. Inspired by a newspaper article about domestic partnerships, Larry asks Chuck to enter a civil union with him. Although Chuck declines at first, he is reminded of his debt to Larry and finally agrees, entering a domestic partnership and becoming Larry's primary beneficiary in the event of his death. To their dismay, however, New York City investigators soon arrive to inquire about their abrupt partnership, under suspicion of fraud. Chuck and Larry decide to enlist the help of lawyer Alex McDonough, played by Jessica Biel, who suggests they get married and move in together to prove they're committed. Chuck reluctantly agrees. The pair soon travel to Canada for a quick marriage (so quick they use a nearby homeless person as the best man) and begin living together.
On the MS Poseidon, a luxury ocean liner, former New York City Mayor and fireman, Robert Ramsey (Kurt Russell), is traveling with his daughter Jennifer (Emmy Rossum) and her boyfriend Christian (Mike Vogel), soon to be engaged. Also on board is professional gambler Dylan Johns (Josh Lucas), architect Richard Nelson (Richard Dreyfuss), Maggie James (Jacinda Barrett) and her son, Conor (Jimmy Bennett), stowaway Elena (Mía Maestro), and waiter Valentin (Freddy Rodriguez).
Dr. Harry Dalton (Pierce Brosnan), a volcanologist of the United States Geological Survey, and his partner Marianne (Walker Brandt), are studying volcanic activity in Colombia when the volcano erupts. Marianne is killed by a piece of falling debris, leaving Harry remorseful about her death, believing it could have been prevented by evacuating sooner.
In 1873, New Mexico Territory, an unnamed loner (Daniel Craig) wakes up in the desert being injured with no memory and with a strange metal object on his wrist. After killing three drifters who think he might be worth bounty money, he takes their clothes, weapons and a horse. He wanders into the small town of Absolution where the local preacher Meacham (Clancy Brown) treats his wound. After the stranger subdues Percy Dolarhyde (Paul Dano), a volatile drunk who has been terrorizing the town, Sheriff Taggart (Keith Carradine) recognizes the stranger as Jake Lonergan, a wanted outlaw, and attempts to arrest him. Jake beats up the posse sent to take him in and nearly escapes, but a mysterious woman named Ella Swenson (Olivia Wilde) knocks him out. Taggart prepares to transport both Jake and Percy to Santa Fe for trial.
Newly elected to Congress, former local television news reporter Evan Baxter (Steve Carell) leaves his hometown of Buffalo, New York and moves to suburban northern Virginia, where his congressional campaign declares that he will change the world. Evan prays to God (Morgan Freeman) to give him this opportunity. On the other hand, his wife, Joan (Lauren Graham), expresses her concern about the new location and prays that she, Evan, and their three sons (Jimmy Bennett, Graham Phillips, and Johnny Simmons) will be closer together as a family. On the first day of his job, Evan is given a prime office space, where he is accompanied by his three congressional staffers, Rita, Marty, and Eugene (Wanda Sykes, Jonah Hill, John Michael Higgins), and invited to co-sponsor the Public Land Act bill with his boss, Chuck Long (John Goodman).
In 1993, following the ousting of the central government and start of a civil war, a major United Nations military operation in Somalia is authorized with a peacekeeping mandate. After the bulk of the peacekeepers are withdrawn, the Mogadishu-based militia loyal to Mohamed Farrah Aidid have declared war on the remaining UN personnel. In response, U.S. Army Rangers, Delta Force counter-terrorist operators, and 160th SOAR aviators are deployed to Mogadishu to capture Aidid, who has proclaimed himself president of the country.
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.
A deadly virus wipes out almost all of humanity in 1996, forcing remaining survivors to live underground. In 2027, James Cole (Willis) is a prisoner living in a subterranean shelter beneath the streets of Philadelphia. Cole is selected for a mission, where he is trained and sent back in time to collect information on the virus in order to help scientists develop a cure. Meanwhile, Cole is troubled by recurring dreams involving a foot chase and an airport shooting.
While moving a train pulled by engines #777 and #767 at the Veteran Allegheny and West Virginia Railroad (AWVR) trainyard in the fictional city of Fuller Pennsylvania, the two hostlers Dewey and Gilleece take ill-advised shortcuts and accidentally allow the engine to leave the trainyard on its own power without the air brakes engaged. Initially believing the train to be a "coaster", yardmaster Connie Hooper orders Dewey, Gilleece, and chief welder Ned Oldham to drive and catch up the train to stop it. When Oldham finds that the train has already past where it was supposed to be, they realize that the train is running on full power and now poses a dangerous threat. Dewey and Gilleece manage to catch up to 777 using a high-railing truck, but fail to board the train in time. Hooper alerts Oscar Galvin, director of operations for AWVR, as well instructs the local and state police and sheriffs to secure all the grade crossings to prevent injury. Visiting Federal Railroad Administration safety inspector Scott Werner finds that 8 cars being pulled by 777 contain molten phenol which would be a major disaster if the train should crash or derail in a populated area. News of the runaway train soon becomes a media event.
In 1957 Brooklyn, New York, Rudolf Abel retrieves a secret message from a park bench and reads it just before FBI agents burst into his rented room. He prevents discovery of the message, but other evidence in the room leads to his arrest and prosecution as a Soviet spy.
Alex Shaw is on a motorcycle chase after a vehicle with stolen goods. He eventually catches the driver of the vehicle, but his girlfriend Annie runs into him during her driving test. She finds out that Alex is on the SWAT team after he lied and told her he was a beach cop. As an apology, Alex surprises her with a Caribbean cruise on Seabourn Legend.
In New York City's Central Park, people begin committing mass suicide. Initially believed to be caused by a bio-terrorist attack using an airborne neurotoxin, the behavior quickly spreads across the northeastern United States. Elliot Moore, a high school science teacher in Philadelphia, hears about the attacks and decides to go to Harrisburg by train with his wife, Alma. They are accompanied by his friend Julian and Julian's eight-year-old daughter Jess. Julian's wife is stuck in Philadelphia but is expected to meet them in Harrisburg. The train loses all radio contact en route and stops at a small town. They receive word that Philadelphia has been attacked by the toxin and Julian's wife was not able to get on the train to Harrisburg. Julian decides to go look for her, leaving his daughter with the Moores while he hitches a ride. However, the town has already been hit by the toxin. Succumbing to it, the driver and Julian both commit suicide.
On September 11, 2001, Port Authority Police officers John McLoughlin and Will Jimeno are patrolling the Port Authority Bus Terminal in Midtown Manhattan when they see a plane fly dangerously low overhead. As all of the police officers return to the station, they see on TV that the North Tower of the World Trade Center has been hit by the plane. Sergeant McLoughlin assigns many of the officers to assist in a precautionary evacuation attempt of the North Tower and they board a Metropolitan Transit Authority bus. On the bus, they hear reports that the South Tower is also hit by another plane. When they arrive at the World Trade Center, they realize the extent of the disaster, and see one of the victims jump out of the towers to certain death. The men proceed to get safety equipment from Building 5 and enter the concourse between the towers.
Airline pilot captain Whip Whitaker (Washington) uses cocaine to wake up after a night of very little sleep in his Orlando hotel room. He pilots SouthJet Flight 227 to Atlanta which experiences severe turbulence at takeoff. Copilot Ken Evans (Geraghty) takes over while Whip discreetly mixes vodka in his orange juice and takes a nap. He is jolted awake as the plane goes into a steep dive. Unable to regain control, Whip is forced to make a controlled crash landing in an open field and loses consciousness on impact.
A group of high school students are in a car together in the night as a storm is brewing. When the storm gets worse, they look up ahead and see a tornado approaching. A girl begs for them to go, but the boy recording on a camera gets out to video tape the tornado. He gets back in the car, but the tornado picks them up before they can escape, killing them all.