Plot
British spy Finn McMissile infiltrates an oil rig in the Pacific Ocean owned by criminal lemon cars to rescue fellow spy Leland Turbo. He witnesses the lemons, seemingly led by Professor Zündapp, loading an emitter disguised as a television camera onto a shipping crate. Upon discovering Turbo's death, Finn is exposed and he escapes by faking his death.
After winning his fourth Piston Cup honoring his late mentor Doc Hudson, Lightning McQueen returns to Radiator Springs to spend the off-season with his friends. Italian formula race car Francesco Bernoulli challenges Lightning to participate in the World Grand Prix, an international three-race event created by former oil tycoon Sir Miles Axlerod, who intends to promote his new environmentally friendly fuel, Allinol. Lightning and his best friend Mater, along with Luigi, Guido, Fillmore, and Sarge, depart for Tokyo, where the first race takes place.
At a World Grand Prix promotional event, Mater makes a scene after eating wasabi and seemingly leaking oil on stage, embarrassing Lightning. Forced to head for a bathroom, Mater accidentally interrupts a fight between American spy Rod "Torque" Redline, who is tasked with handing Finn intel, and lemons Grem and Acer. Redline plants a device on Mater, causing Finn and his associate Holley Shiftwell to believe Mater is their contact. Meanwhile, Redline is captured and killed by Zündapp, who reveals that Allinol ignites when hit with an electromagnetic pulse. He informs his superior, an unknown mastermind, that Redline passed on his information. Holley recruits Mater to stop Zündapp's plot, believing him to be an undercover agent.
During the race, three racers are ignited by the camera. Lightning places second due to miscommunication with Mater, who was evading Zündapp's henchmen with Holley's instructions. Lightning confronts him at the pits, snapping at him and declaring he doesn't want his help. A guilt-ridden Mater prepares to return to Radiator Springs but is taken by Finn, and they escape from the lemons in his jet, Siddeley. After traveling to Paris to gather intel from Finn's old friend Tomber, they go to Porto Corsa in Italy, where the second race takes place. Mater infiltrates the lemons' meeting as the camera ignites several more racers, causing a multi-car pile-up, while Lightning wins. Due to controversy over Allinol's safety, Axlerod lifts its requirement for use in the final race in London. When Lightning decides to continue using it, the lemons plan to kill him. This spooks Mater into blowing his cover, causing him, Finn, and Holley to be captured and tied up inside Big Bentley, where he admits to them that he is not the spy they think he is.
As the race starts, Lightning takes the lead before passing Big Bentley, but the camera inexplicably does not ignite him. The lemons tell Mater that they planted a time bomb in Lightning's pits as a backup plan, spurring him to escape. Finn and Holley soon follow, but they realize the lemons fitted the bomb on Mater's air filter instead. As Mater is informed of this, he flees down the track and Lightning pursues him to apologize for his outburst, while Finn apprehends Zündapp. The other lemons arrive and outnumber Finn, Holley, Mater, and Lightning, but they are rescued by the other Radiator Springs residents and Sarge's colleagues in the British Army. Mater and Lightning go to Buckingham Palace, where Mater exposes Axlerod as the mastermind, proven when he is forced to disable the bomb. It is revealed that the World Grand Prix was Axlerod's cover-up to turn the world against alternative fuels and profit from his ownership of the world's untouched oil reserves. Axlerod and the lemons are arrested, Mater receives an honorary knighthood from the Queen, and he and Lightning reconcile.
Back in Radiator Springs, as Mater tells everyone about his experience, Fillmore reveals that Sarge swapped Lightning's Allinol with Fillmore's biofuel prior to the London race, explaining the camera's ineffectiveness on Lightning. A "Radiator Springs Grand Prix" is held, featuring the World Grand Prix contenders. Finn and Holley invite Mater to go on another mission, but he declines. While his weapons are confiscated, Mater keeps the rockets and speeds off with Lightning and the other racers, as Siddeley flies into the distance.
