The movie begins on the last day of summer, Christopher Robin does not have the heart to tell Winnie the Pooh of his departure to school the next day. Although the two have fun playing the whole day, Christopher Robin is unable to tell Pooh where he's going, and leaves him with the advice, “You're braver then you believe, stronger then you seem, and smarter then you think.”
Meanwhile, British spy Finn McMissile infiltrates the world’s largest untapped oil reserves, owned by a group of “lemon” cars. After being discovered, he is forced to flee and fake his death.
Back in the Hundred Acre Woods, the first day of Autumn has arrived; to Winnie the Pooh it’s another fun-filled season to be with his very best friend, Christopher Robin. However, he is nowhere to be found, which causes Pooh to worry what happened to him. After finding a sticky note revealing that Christopher Robin has been kidnapped, Owl scares Pooh, Piglet, Tigger, Rabbit, Eeyore, The Vultures, Jiminy Cricket, Zazu, Kronk, SpongeBob SquarePants, Patrick Star, Squidward Tentacles, Sandy Cheeks, Mr. Krabs, Alex, Marty, Melman, Gloria, Skipper, Kowalski, Rico, Private, and the Mighty Morphin Power Rangers when he reveals that Christopher Robin has been kidnapped by Professor Z and the Lemons. Pooh and all the others decided to head into the Cars world to find and save their friend. They all arrive at Radiator Springs and meet again with Mater and decide to wait on their journey to hang out with him.
Then, four-time Piston Cup champion Lightning McQueen returns home to Radiator Springs and reunites with them, Mater and his girlfriend Sally Carrera. Former oil tycoon Sir Miles Axlerod, now a green power advocate, announces a racing series called the “World Grand Prix” to promote Allinol, his biofuel. When Italian formula race car Francesco Bernoulli challenges McQueen, he, Mater, Pooh and the all the others - along with Luigi, Guido, Fillmore and Sarge - depart for Tokyo, Japan for the World Grand Prix.
Meanwhile, the lemons, led by Professor Zundapp and an unknown mastermind, secretly plot to secure their oil profits by using a weapon disguised as a television camera to ignite the Allinol fuel. Finn and partner Holley Shiftwell attempt to rendezvous with American spy car Rod “Torque” Redline at a World Grand Prix promotional event in Tokyo, to receive information about the mastermind; however, Redline is attacked by Zündapp’s henchmen and passes his information to Mater before he is captured. Holley and Finn mistake Mater as their American contact. Zündapp tortures Torque and reveals that Allinol can ignite if impacted by a high electromagnetic pulse. Zündapp demonstrates it on Torque, killing him, but not before they realize that he passed this information to Mater.
During the first race, Finn and Holley help Mater evade Zündapp's henchmen; in the process, Mater inadvertently gives McQueen bad racing advice which causes him to lose the race to Bernouilli. Meanwhile, Zündapp uses the weapon on several race cars. After McQueen falls out with Mater, Finn - who still believes Mater and now even Pooh and all the others are American spies - drafts them into foiling Zündapp's plot. Finn, Mater, Pooh and all the others escape Zündapp's henchmen and climb aboard Siddeley. Finn and Holley remove the tracking device on Mater and discover in it a picture of a mysterious British engine, which Mater identified by the engine and rare parts.
Finn, Holley, Mater, Pooh and all the others fly to Paris, France, where they go into a black-market and meet an old friend of Finn's, Tomber. Finn and Holley show the mysterious engine to Tomber, who tells them that the car with the engine was his best customer, but he has never met him in person. Mater explains what he knows about the evil Lemons, and realizes that every Lemon involved with the plot is one of “history’s biggest loser cars”. Tomber tells Finn, Holley, Mater and our heroes that the lemons are going to have a secret meeting in Porto Corsa, Italy (where the next race in the World Grand Prix is taken place).
In Italy, Mater infiltrates the criminals’ meeting and discovers Zündapp’s plan and even found Christopher Robin held-captured there in the meeting. Zündapp’s henchmen, meanwhile, use their weapon on several more cars during the race, eventually causing a multi-car pileup on the Casino Bridge. With the Allinol fuel under suspicion, Axlerod suspends its use for the final race in England; however, McQueen chooses to continue using it. The criminals decide to kill McQueen in the next race; upon hearing this, Mater is exposed and is captured along with Finn, Holley, Pooh and all the others, and tied up inside Big Bentley’s bell tower in London, England, along with Christopher Robin.
After having a nightmare that showed him his crazy antics in Tokyo during the World Grand Prix while he was knocked out, Mater realizes how foolishly he has been acting. The criminals use the weapon on McQueen during the race, but nothing happens. Mater, Pooh and all the others escape to warn their friends of a bomb planted in McQueen’s pit stop, but Finn and Holley find that the bomb was actually planted on Mater. They warn Mater and our heroes about the bomb, and he, flee to protect their friends. However, they are pursued by McQueen in an attempt to reconcile, unaware of the danger until they are beyond the range of Zündapp's remote detonator. He sends his henchmen to kill McQueen, Mater, but they are foiled by the combined efforts of Finn, Holley, and the Radiator Springs residents. Upon his capture, Zündapp reveals that only the person who installed the bomb can deactivate it, and Mater realizes that Axlerod is the mastermind behind the plot. Mater confronts Axlerod, trapping him next to the bomb. Axlerod finally deactivates the bomb, and he, Zündapp and the lemons are arrested by the police.
As a reward for his heroism, Mater receives an honorary knighthood from the Queen and Princess Celestia and returns home with his friends, where the cars from the Grand Prix take part in the unofficial Radiator Springs Grand Prix. Fillmore reveals that before the last race, Sarge replaced McQueen’s Allinol with Fillmore's organic fuel, which prevented McQueen from being affected by the weapon. Finn and Holley invite Mater, Pooh and the others to join them in another spy mission, but they graciously turn it down but Mater asks Holley for a date when she returns which she accepts. Pooh and the others all thanked Finn and Holley for helping them and Mater for finding and rescuing Christopher Robin, who also thanked them for helping them finding and rescuing him. Then, Mater gets to keep the rockets Finn and Holley gave him earlier, which he uses in the Radiator Springs race.
- Tennessee Tuxedo, Chumley, Garfield, Odie, Poky Little Puppy, Shy Little Kitten, Tip, Dash, Ash Ketchum, Pikachu, Misty, Togepi, Brock, Littlefoot, Cera, Ducky, Petrie, Spike, Chomper, Ruby, Guido, Grandpa Longneck, Grandma Longneck, Skip, Mr. Thicknose, SpongeBob SquarePants, Patrick Star, Squidward Tentacles, Sandy Cheeks, Mr. Krabs, Alex, Marty, Melman, Gloria, The Penguins of Madagascar (Skipper, Kowalski, Rico, and Private), Princess Twilight Sparkle, Spike the Dragon, Pinkie Pie, Applejack, Rainbow Dash, Rarity, Fluttershy, Starlight Glimmer, The Cutie Mark Crusaders (Apple Bloom, Sweetie Belle and Scootaloo), Princess Cadance, Shining Armor, the Mighty Morphin Power Rangers and Christopher Robin are guest starring in this film.
- The storyline concludes in Pooh's Adventures of Cars 3.
- This film featured a special version of the Vultures' song, That's What Friends Are For, where Pooh and the gang (along with Jiminy Cricket, Zazu, Kronk, Zhane, Korra, Mako, Bolin, Asami Sato, Jeremy the Crow, Jean-Bob, Speed, SpongeBob, Patrick, Squidward, Sandy, Mr. Krabs, Alex, Marty, Melman, Gloria, Skipper, Kowalski, Rico, Private, and the Mighty Morphin Power Rangers) sing along with the Vultures.
- Princess Celestia makes a special appearance near at the end of the film (during the whole thing taking place in London); she was a special friend of The Queen and she came to see the World Grand Prix.
- During the film, Pooh, Ash, Littlefoot, SpongeBob, Alex, Skipper, Princess Twilight, Tommy and all the others go with Mater to join Finn McMissile and Holley Shiftwell on their special mission about the Lemons and rescuing Christopher Robin.
- Bowser Koopa will be mentioned in this film.
- The film takes place before Pooh's Adventures of Les Miserables (2012).
- This film takes place after 76859Thomas' film, Pooh's Adventures of My Little Pony: Friendship is Magic - The Cutie Re-Mark (Full Movie) (winch Starlight Glimmer joins the mane 6).
- Both Winnie the Pooh and Cars 2 were released in theaters in 2011.
- and Cars 2 are all made by Disney.