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." The next morning, Pooh discovers a honey pot with an attached note - however, he cannot read it himself. As he goes around to his friends Tigger, Piglet, Rabbit and Eeyore, it's clear that the group needs Christopher Robin's help and advice with their own obstacles, and none of them are able to read it. Owl "deciphers" the writing on the note, and reports that Christopher Robin has been kidnapped by Professor Ratigan and was taken to London. Pooh and his friends decided to head to London to save their friend.
In London, circa 1897, a young Scottish mouse named Olivia Flaversham is celebrating her birthday with her Toymaker father, Hiram. Suddenly, Fidget, a crippled bat with a peg leg, kidnaps Hiram. Fidget takes Hiram to Professor Ratigan who commands him to create a clockwork robot which mimics the Queen of the Mice so Ratigan can rule England and have Christopher Robin as bait. Hiram and Christopher refuse to take part in the scheme, whereupon Ratigan orders Fidget to capture Olivia and Pooh so he can feed them to his pet cat, Felicia.
Olivia searches to find Basil of Baker Street, a world-famous detective and Ratigan's archnemesis. Returning to London after a tour of duty in Afghanistan, Dr. David Q. Dawson stumbles upon Olivia and Pooh and his friends, and helps her find Basil's residence. At first, Basil is reluctant, but when Olivia mentions Fidget, Basil realizes his chance to capture Ratigan. Basil and Dawson take Toby, Sherlock Holmes's pet dog, to track Fidget's scent, where they find him in a toyshop stealing clockwork mechanisms and toy soldiers' uniforms. Fidget later traps Olivia and Pooh by ambushing them from inside a toy cradle. Basil, Dawson, Piglet, Tigger, Rabbit, and Eeyore pursue Fidget, but become entangled and fall behind. While searching the shop, Dawson discovers Fidget's checklist, to which Basil does some chemical tests to discover the list came from the riverfront near the Thames. Basil, Dawson, Piglet, Tigger, Rabbit, and Eeyore disguise themselves as sailors and go into a tavern called the "Rat Trap" and follow Fidget to Ratigan's headquarters. They along with the others are caught, and Ratigan ties them to a spring-loaded mousetrap connected with a Rube Goldberg machine. Ratigan sets out for Buckingham Palace, where Fidget and his accomplices kidnap the queen. Basil, Dawson, and the others deduces the trap's weakness and escape just in time.
Back at Buckingham Palace, Ratigan forces Hiram to operate the toy Queen, while the real Queen is taken to be fed to Felicia. The toy Queen declares Ratigan the ruler of all Mousedom, and he announces his tyrannical plans for his new "subjects". Just then, Basil, Dawson, Olivia, and Pooh and his friends save Hiram, Christopher, and the real Queen, and apprehend Fidget (along with Ratigan's other henchmen). Basil forces the mechanical queen to denounce Ratigan as an impostor and tyrant while breaking into pieces. The crowd, enraged by Ratigan's treason, start climbing onto him and defeating his shanty guards. Ratigan frees himself and escapes on his dirigible with Fidget, holding Olivia hostage. Basil, Dawson, Hiram, and our heroes create their own craft with a matchbox and some small helium-filled balloons, held under the Union Jack. Ratigan throws Fidget (who can't fly) into the Thames River, and then attempts to drive the dirigible himself. Basil and Pooh jump on to the dirigible to confront Ratigan, causing him to crash straight into the Big Ben. Inside the clock, Basil and Pooh rescue Olivia and safely delivers her to Hiram. Ratigan fights Basil and Pooh until the clock bell tolls and Ratigan plunges, taking Basil with him. However, Basil manages to save himself just in time.
Back at Baker Street, Basil, Dawson, and our heroes recount their adventures, as well as the queen's gratitude for saving her life. Afterwards, the Flavershams leave to catch their train. As Dawson tries to leave, a distraught new client persuades both Basil and Dawson to help her. Finally, Basil proclaims Dawson to be his "trusted associate, Doctor Dawson, with whom I do all my cases".
- Reese Ambler, Rydell, Ash and his friends, Mickey Mouse and his friends, Max Goof, Roxanne, Scrooge McDuck and his family, the Looney Tunes, Simba, Timon, Pumbaa, Ronald McDonald and his friends, Earl Sinclair and his family, Oobi, Uma, Kako, Grampu, Bloom and her friends, Captain Underpants, George Beard, Harold Hutchins, Clifford, Cleo, T-Bone, Mac, Emily Elizabeth, Charley, Jetta, Godzilla, Godzooky, Little Godzilla, Minilla, Anguirus, Rodan, Mothra, the Tiny Toons, Blard Simpleton, Maya and Miguel's family, Dink the little dinosaur and his friends, the Kids Next Door, Numbuh 362, Sharon Spitz and her friends, Richie Cummingham and his friends (from Happy Days), Frank Phil, IG-88 and his friends, Dr. Alan Grant and his friends, Kanga, Roo, Lumpy, the Bowser family, Azula Team Rocket Jessie James Mewoth , Dr. Facilier, the Crime Empire, the Super Evil Squad, Nostalgia Critic, the TGWGT Squad, the Angry Video Game Nerd, the Ancient Minister, Asajj Ventress, King Dedede, Escargoon, the Star Wolf team, Deputy Einstein, Professor Poopsie P. Pottypants, Kaput, Zosky, One-Eyed Sally, Blather, King Ghidorah, SpaceGodzilla, Gigan, Megalon, Father, the Delightful Children, Tyrannor, the Predator, Scar, Shenzi, Banzai, Ed, Arthur, Cecil, Mortimer Mouse, Pete, Icy, Darcy and Storm) Guest Stars In This Film
- This is an NTSC film with NTSC bits from The Many Adventures of Winnie the Pooh, The Tigger Movie,Winnie the Pooh: A Very Merry Pooh Year, and Pooh's Heffalump Movie and PAL bits from Pooh's Grand Adventure: The Search For Christopher Robin Piglet's Big Movie. And Many Other Movies