Thomas & The Discovery of Sodor is a American-British photo-puppetry animated/model comedy-musical fantasy film. It was a crossover between Thomas the Tank Engine & Friends and The Wonder Pets. This film was released in theaters in January 5, 1999. Distributed by Walt Disney Pictures, Little Airplane Productions and Britt Allcroft Productions.
Linny (from The Wonder Pets) begins the story that happened last week. This is the story about trains, pets far apart and the discovery that we have seen! One summer day, Thomas is seen telling James that Linny the Guniea Pig will look after us, while Sir Topham Hatt is visiting his foster father at her house for a month. Suddenly, a biggest diesel with 5 claws named Diesel 5000 roars past the two engines. James is horrified about this. But Thomas calms him down, and says that they will rid that diesel if he keeps up his bad behaviour.
Far away from Sodor, is the schoolhouse the Wonder Pets live. The Wonder Pets enjoy doing things they like such as dancing, playing roles of other people and more. Thomas is still worried about a Diesel 5000, and goes back to the shed where he finds Donald and Douglas arguing about Douglas's coal accident. He tries to tell them about Diesel 5000 when the mean diesel arrives at the yard, which he threatens to destroy a lost steam engine named Man, then to devour Sir Topham Hatt at his foster father's house, and then replace him as his new controller. Thomas, Donald and Douglas are horrified at such idea and will not like that, thanks to Sir Topham Hatt. Thomas tries to warn Diesel 5000 not to do bad things, like Duck just told the rest of the engines.
At the schoolhouse (seen on The Wonder Pets), Ollie is seen talking to a harmless snake named Mutt about the cleaness of the school playground. Then, Tuck arrives and he and Ollie go to find a lost steam engine. It is revealed that it has fallen off a cliff and into the ground, smashing into pieces. His face is now gone, fading to a smokebox door. Linny, at the schoolhouse room, is seen talking to Ming Ming that she will go to the Island of Sodor to look after Sir Topham Hatt's engines while he is visiting his foster father's house for a month. She blows her goldust whistle and disappears.
Later Thomas is looking for Linny and finally finds her. Linny hops on Thomas' cab. The two go to the yards and warn the other engines about Diesel 5000. The engines are busy avoid the evil diesel. Later, Linny and the engines are asleep, till suddenly, Linny finds that her goldust is gone and tries looking for it. The next morning, Linny's cousin named Wilbur (voiced by Dean DeLuna), who is 5 years old, arrives on the schoolhouse classroom and remembers everything he likes to do. He soon knows that Man is broken in a crash. Ollie grandfather Pete has been working on it. Nightime came, and Thomas, Edward, Percy, Toby, Duck and BoCo are talking in the sheds about Diesel 5000. Meanwhile the same night, Diesel 5000 is seen talking to his sidekicks Winston and Zinston about destroying the lost engine and Sir Topham Hatt. When Diesel 5000 hears BoCo's horn and plans to smash him, but instead makes the shed fall on him and his sidekicks.
The next morning, Duck is collecting freight cars to take at the Harbour, and finally delivers it there. James is there, and is grumbling about pulling coal cars, saying empty cars and passenger coaches are better. Duck tries to tell him that he should stop complaining. James refuses to believe that, and puffs off. At the coal hopper, Diesel 5000 tries to show Winston and Zinston how to handle coal cars, but accidentally hits the chute, sending coal all over Diesel 5000. He coughs, while Thomas, Percy, Duck and Toby laugh at this.
Meanwhile, Ollie and Tuck find Pete and explain about the lost engine, since Pete tried working on him. Back on Sodor, Linny is trying to find the source of the goldust when Diesel 5000 appears behind her, grabs her and takes her the side of the cliff. Soon. Linny has an idea, she cuts one of the pipes connected to one of Diesel 5000's claws she's on. The claw springs open and throws Linny at bags of flour at the base of the windmill.
Later, Wilbur Tuck, Ming-Ming and Ollie travel to the Island of Sodor. They find Linny at the windmill. Linny explains what happened earlier when she saw Diesel 5000 and was thrown in there. Thomas, Edward, Percy, Duck, Toby and BoCo has seen her in there and knows that she is fine too. Linny goes to talk to Sir Topham Hatt on the flower phone. After the conversation on the phone is done, The engines and the Wonder Pets find that Wilbur is on the windmill. It spins him out and he lands on the top of Diesel 5000! The engines are shocked, so are the Wonder Pets.
Wilbert, suddenly, arrives and has news for all the engines that one of the coal cars Diesel 5000 sent are in the Magic Line. Percy volunteers, and he and Ollie set off to find the missing coal car and Pete. They arrive at the magic line and look for the missing coal car. Percy sees it and couples to the it and pulls it all the way to Magic Mountain Line. They arrive there, and Ollie leaves Percy on the mountain line, who claims that his wheels won't let him move. Suddenly, Diesel 5000 uses his claw to set off an explosion on the bottom of the mountain, and an explosion causes Percy to slide down the mountain rails, towards an edge of a grassy cliff and falls into a field, finding himself stuck in a pile of wet mud. Thomas hears the crash and puffs off to get the breakdown train.
Ollie soon reunites with his grandfather. They soon lift Man onto a flatbed of a large crane and take it to the works to have it fixed. After that, it was good as new, so is Percy, whose wheels, siderods, buffers and green paint have been cleaned. Thomas, Edward and Duck are there too. The Wonder Pets, Thomas, Edward, Duck and Man puff to find Diesel 5000, and see him on a large mountain cliff. First Duck shunts Winston and Zinston off an viaduct and into the ravine. Then, Thomas steams to the back of Diesel 5000 and shunts him off the right side of the cliff. Diesel 5000 lands onto a river of acid. He melts and burns away screaming "I'M MELTING, MELTING!!". The diesels are gone. And everyone goes to the lair of the diesels. Linny has her goldust back, and the movie ends with everyone celebrating.
- The musical arrangements for the movie are from "Honey I Shrunk the Kids".
- When Linny screams as she is thrown into bags of flour at the base of the windmill, her scream is Sagwa's scream from "Treasure Hunters" (when Sagwa and her friends run away from the boulder, after Sagwa says "FASTER!!").