In 2009, American geologist Adrian Helmsley visits astrophysicist Satnam Tsurutani in Jharkhand, India, and learns that a previously undiscovered type of neutrino from a solar flare is heating the Earth's core. Returning to Washington, D.C., Adrian alerts White House Chief of Staff Carl Anheuser and President Thomas Wilson. A year later, over forty-six nations led by the G8 and China begin building nine arks in Tibet, while storing artifacts aboard them. Nima, a Buddhist monk, is evacuated with his grandparents, while his brother Tenzin joins the ark project. Additional funding is secretly raised by selling tickets to the rich for €1 billion per person. In 2012, struggling science-fiction writer Jackson Curtis is a chauffeur in Los Angeles for Russian billionaire Yuri Karpov. Jackson's former wife, Kate and their children, Noah and Lilly, live with Kate's boyfriend, plastic surgeon and amateur pilot Gordon Silberman. Jackson takes Noah and Lilly camping at Yellowstone National Park. When they find Yellowstone Lake dried up and fenced off by the United States Army, they are caught and brought to Adrian. They later meet conspiracy theorist and radio personality Charlie Frost, who tells Jackson of Charles Hapgood 's earth crust displacement theory and how the Mesoamerican Long Count calendar predicts the end of the world in 2012, and that the world's governments silence anyone attempting to warn the public. Despite his initial skepticism, Jackson begins to take Charlie's warning seriously after witnessing several signs that seem to confirm it. These include a conversation with Yuri's sons, Alec and Oleg, who warn of impending disaster after Jackson drops them off at Santa Monica Airport. He rents a Cessna 340A and sets out to rescue his family. As the Pacific Coast suffers a catastrophic 10.9-magnitude earthquake along the San Andreas Fault, Jackson and his family reach the airport and escape aboard the Cessna before the coast sinks into the Pacific Ocean. The group flies to Yellowstone, and Jackson retrieves Charlie's map of the Arks' location, just as the Yellowstone Caldera begins to erupt. Charlie stays behind to finish his broadcast and is killed by debris. Realizing they need a larger plane to fly to the Himalayas, the group lands at McCarran International Airport in Las Vegas to locate one. Adrian, Carl, and First Daughter Laura fly to the arks while President Wilson remains in the White House to address the nation. Jackson finds the Karpovs, Yuri's girlfriend Tamara, and their pilot, Sasha. Sasha and Gordon fly the families out in Yuri's Antonov An-500, as the volcanic ash from Yellowstone envelops Las Vegas. The planet's crust shifts, resulting in billions of deaths in disasters worldwide, including President Wilson. With the presidential line of succession broken, Carl appoints himself acting commander-in-chief. Upon reaching the Himalayas, the Antonov's engines malfunction. As the plane touches down on a glacier, the party uses a Bentley Flying Spur stored in the hold to escape, while Sasha stays in the cockpit and is killed when the jet goes over a cliff. The survivors are spotted by Chinese Armed Police helicopters which take only the three ticket-bearing Karpovs, and Yuri reveals his knowledge of Tamara and Sasha's affair, leaving Jackson's family and her behind. The group encounters Nima, who, with his own family, takes them to the arks, where they stow away on Ark 4 with Tenzin's help. With a megatsunami approaching, Carl orders the loading gates closed, though many people have not yet boarded. Adrian persuades the captain and the other surviving world leaders to allow more passengers aboard the arks, while Yuri falls to his death as he pushes his sons onto Ark 4. As the gate closes, Tenzin is injured and Gordon is fatally crushed. Tenzin's impact driver lodges in the gate mechanism, preventing it from closing completely and disabling the ship's engines. As the tsunami strikes, the ark starts flooding as it is set adrift, heading for Mount Everest. Adrian rushes to clear the gears, but watertight doors close, trapping the stowaways and drowning Tamara. Noah and Jackson dislodge the tool, and the crew regains control of the ark. Twenty-seven days later, the waters start receding. The arks approach the Cape of Good Hope, where the Drakensberg Mountains are now the highest mountain range on Earth. Adrian and Laura begin a relationship, while Jackson and Kate reconcile.

In Manila, a terrorist assassinates the United States Ambassador to the Philippines, and also kills his son and dozens of children at an international primary school in a terrorist bombing. The mastermind, a Chechen terrorist, Abu Shabal, escapes to a training camp in Indonesia. Elsewhere in Costa Rica, two CIA officers, Walter Ross and Lisa Morales, meet to consolidate intelligence about their target, a drug smuggler named Mikhail "Christo" Troykovich. Christo's men kill Ross and capture Morales, who is imprisoned in a jungle compound and tortured. At Coronado, the members of Bandito Platoon, SEAL Team 7 are at home. Lieutenant Rorke confides to Chief Dave that his wife is pregnant and has the entire team spend time together with their families until their next deployment. A squad from the platoon consisting of Rorke, Dave, Wiemy, Mikey, Ray, Sonny, and Ajay, is then deployed to Costa Rica to exfiltrate Morales. The SEALs insert into the jungle via HALO and hold position outside the compound all night. At dawn, they raid the compound and eliminate several guards before extracting Morales and a cell phone containing the information she had gathered. Alerted by the assault, an enemy quick reaction force attempts to pursue and the SEALs commandeer a truck to exfiltrate. The pursuit forces them to revert to a tertiary extraction point where two SWCC boats extract the team, with Mikey being wounded in action. Christo and Shabal, who are revealed to have been childhood friends, meet in Kyiv. Christo knows the CIA is watching him and informs Shabal that subordinates will complete their project, which is to equip suicide bombers with specialized undetectable explosive vests. On the amphibious assault ship USS Bonhomme Richard, Rorke is informed that the intelligence recovered confirms Shabal and Christo were working together. Shabal seeks to bring jihad to the U.S., while Christo provides the routes for smuggling drugs and people into the U.S. Ajay and Ray are sent to Somalia, where an arms transfer involving Shabal is taking place. The remaining SEALs, comprising Rorke, Dave, Sonny and Weimy, stay in the U.S. in case the terrorists make it in. Miller himself has been reassigned to SEAL Team Four, hunting for Christo somewhere on the oceans. Lieutenant Rorke gives Dave a letter to give to his family in case he is killed. Shabal and sixteen terrorists are found to be on an island off Baja California, where the SEALs act to secure the island, killing eight terrorists. Shabal and eight others escape. Elsewhere, in the South Pacific, SEAL Team Four captures Christo and interrogate him, learning that Shabal's plot is to outdo the September 11 attacks. The SEALs are informed that Shabal is en route to the U.S. via tunnels underneath a milk factory, and are ordered to link up with Mexican Special Forces and neutralize the remaining targets. Arriving at the factory, the SEALs and Mexican forces launch an assault there, engaging numerous Mexican cartel members and Shabal's terrorists in the process. During the gunfight, a combatant throws a grenade, and Rorke sacrifices himself by diving on it to save his team before it detonates, killing him. Dave pursues the terrorists and shoots them as they try to escape through the tunnels. He is then shot several times and gravely wounded by Shabal, who is intercepted and killed by Sonny before he can execute Dave. At home, Rorke is given a military funeral with full honors, where the SEALs pay their respects. It is then revealed that Dave's narration throughout the movie was a written letter meant for Rorke's son. The film ends with a dedication to 60 U.S. Navy SEAL and Special Warfare Combatant-craft Crewmen (SWCC) killed in action since 9/11 along with a listing of their names as well as a photo montage of fallen public servants.

In 1978, Irving Rosenfeld and Sydney Prosser work together as con artists. Sydney, posing as English aristocrat "Lady Edith Greensly", has improved the scams. Irving loves Sydney but is unwilling to leave his unstable, histrionic wife Rosalyn, fearing that he will lose contact with adopted son Danny. Rosalyn has also threatened to report Irving to the police if he leaves her. FBI agent Richie DiMaso catches Irving and Sydney in a loan scam but offers to release them if Irving can line up four additional arrests. Richie believes that Sydney is English but has proof that her aristocratic claim is fraudulent. She tells Irving that she will manipulate Richie, which distances her from Irving. Irving's friend pretends to be a wealthy Arab sheikh looking for potential investments in America. An associate of Irving's suggests that the sheikh do business with Mayor Carmine Polito of Camden, New Jersey, who is trying to revitalize gambling in Atlantic City but has struggled to find investors. Carmine seems to have a genuine desire to help the area's economy and his constituents. Richie devises a plan to make Mayor Polito the target of a sting operation despite the objections of Irving and of Richie's boss Stoddard Thorsen. Sydney helps Richie manipulate an FBI secretary to make an unauthorized wire transfer of $2 million. When Stoddard's boss Anthony Amado hears of the operation, he praises Richie's initiative, pressuring Stoddard to continue. Carmine leaves the meeting when Richie presses him to accept that cash bribe. Irving convinces him the sheikh is legitimate, expressing his dislike of Richie, and they become friends. Richie arranges for Carmine to meet the sheikh, and without consulting the others, has Mexican-American FBI agent Paco Hernandez play the sheikh, which displeases Irving. Carmine brings the sheikh to a casino party, explaining that mobsters are there and that it is a necessary part of doing business. Irving is surprised to hear that Mafia boss Victor Tellegio, right-hand man to Meyer Lansky, is present and wants to meet the sheikh. Tellegio explains that the sheikh needs to become an American citizen, and that Carmine will need to expedite the process. Tellegio also requires a $10 million wire transfer to prove the sheikh's legitimacy. Richie confesses his strong attraction to Sydney but becomes confused and aggressive when she drops her British accent and admits to being from Albuquerque, New Mexico. Rosalyn starts an affair with mobster Pete Musane, whom she met at the party. She mentions her belief that Irving is working with the IRS, causing Pete to threaten Irving, who promises to prove that the sheikh's investment is real. Irving confronts Rosalyn, who admits that she told Pete and agrees to keep quiet but wants a divorce. With Carmine's help, Richie and Irving videotape members of Congress receiving bribes. Richie assaults Stoddard in a fight over the money and soon convinces Amado that he needs the $10 million to get Tellegio, but he gets only $2 million. A meeting is arranged at the offices of Tellegio's lawyer Alfonse Simone, but Tellegio does not appear. Irving visits Carmine and admits to the scam but says that he has a plan to help him. Carmine throws Irving out, and the loss of their friendship deeply upsets Irving. The federal agents inform Irving that their $2 million is missing and that they have received an anonymous offer to return the money in exchange for Irving and Sydney's immunity and a reduced sentence for Carmine. As it turns out, Alfonse Simone, with whom Richie had arranged the wire transfer, was a con man working with Irving and Sydney. Amado accepts the deal, and Stoddard removes Richie from the case, which ends his career. The congressmen are prosecuted, and so is Carmine, who is sentenced to 18 months in prison. Irving and Sydney move in together and open a legitimate art gallery, while Rosalyn lives with Pete and shares custody of Danny with Irving.