Diesel 10 is an evil diesel with a roof-top, hydraulic claw named "Pinchy".
Diesel 10 returned many years later, intending to destroy Lady for good. He brought with him two lapdogs, Splatter and Dodge, who were present when the boss was scheming. He was first seen in the movie charging past Thomas and Gordon at Killaban. He also dumped sneezing powder all around Tidmouth Sheds so that the wind from Harold's blades would blow it all over the place. Diesel 10 had very little success with his plans, and during a speech on "how to stop being stupid", he caused a coal chute to empty its contents on top of him at The Coaling Plant.
By using special coal from Sodor, Lady was able to steam properly again. Diesel 10 was determined to attack her, but lost the aid of Splatter and Dodge. Lady and Thomas found themselves being chased by Diesel 10 over an unsafe viaduct. The center of the viaduct collapsed, and while Thomas and Lady were able to cross safely, Diesel 10 was too large and fell into a passing barge below.
How Diesel 10 got back to Sodor is a mystery. It is likely that Sir Topham Hatt decided to give him another chance.
Thomas and Mavis went to tell steam engines and diesels all over the island to meet at the coaling plant, a chance and hope for them to work together and get the new Sodor Airport built on time. When Thomas went over to tell Diesel 10 about the meeting, he got scared to his wheels. Not sure if Diesel 10 would want to help the steam engines anyway, due to their difficulties in the past, Thomas sped away as fast as he could.
Construction of the airport was almost complete when a tower collapsed, cracking the runway and blocking the tracks. With Harvey too far away to clear the line, Thomas took a chance and decided to ask Diesel 10. Convincing his former archenemy that helping the other engines would prove how useful he was, Thomas returned with help to clear the line.
Diesel 10 and a number of other Diesels later waited in the quarry yard to hear if Thomas had been found in the days leading up to the reopening of Great Waterton.
He later tricked a lonely Percy into helping him take over the Sodor Steamworks. When Percy had a falling-out with Thomas, Diesel 10 used him to attempt to have the Sodor Dieselworks repaired. After convincing Thomas to go to the Dieselworks, Diesel 10 had Percy lead him and the other Diesels to the Steamworks. When they arrived, Diesel 10 betrayed Percy and took over the Steamworks.
When Percy went to the Dieselworks to rescue Thomas, Percy saw that sparks from "Pinchy" had set the main shed ablaze. After saving Thomas and putting out the fire, Percy led the steam engines to the Steamworks. After a brief argument between the engines, the Fat Controller arrived. Percy told him that the Diesels needed a new Dieselworks, so the Fat Controller had the steam engines and Diesels work together to rebuild it.
Diesel 10 stole Christmas decorations from the Steam Team at Tidmouth Sheds with Paxton's help because he thought no one liked diesels. That afternoon, Percy caught him stealing the last of the decorations and bravely raced after the evil diesel in an attempt to get the decorations back, enlisting Edward, Thomas, James, Henry, Gordon, Toby, and Emily to help him. After taking back the decorations, Paxton told Diesel 10 that Sir Topham Hatt gave them a truckload of decorations for the Dieselworks. At the end, he decided to give the Steamies back the decorations, though most of them were crushed by Pinchy, so to compensate, he gave them the diesels' decorations because they considered Sidney to be a good enough decoration.