Diesel 10 has finally returned to Sodor after a long time and is treatening to come up with his most evil plans to get rid of the steam engines forever.
One perfectly normal day, the Steam Team were doing their jobs until Diesel 10 arrived. He was treatening to get rid of the steamies. He was mean to the Steam Team and then left. That night, the Steam Team talked about Diesel 10's return. They were worried about what he would do. Nia and Rebecca didn't know anything about Diesel 10 so the other engines told them about him. Rebecca thought Diesel 10 sounded like a cool engine but the other engines ignored her. They soon decided to not worry about Diesel 10 and went to sleep. Meanwhile, Diesel 10 was at his mountain where he reunited with his former helpers, Splatter and Dodge. Diesel 10 explained what they would do in the future. Splatter and Dodge then told Diesel 10 what they were doing before Diesel 10 came to get them. They worked at a place on the Mainland with other diesels for a long time. They missed being evil and were lucky when Diesel 10 found them. Diesel 10 left Sodor after the time he stole the Christmas decorations from Tidmouth Sheds and travelled to the Mainland to look for Splatter and Dodge. It took him years to track them down but he soon found them and they came back to Sodor together. Diesel 10 was happy to have his helpers back and couldn't stop thinking about what they would do.
- Diesel 10
- Splatter and Dodge
- Annie and Clarabel (do not speak)
- Henry (cameo)
- Caitlin (cameo)
- Connor (cameo)
- Sir Topham Hatt (mentioned)
- It is revealed that Diesel 10 went to the Mainland after the events of the Thomas & Friends episode, The Missing Christmas Decorations to find Splatter and Dodge.
- It is also revealed that Diesel 10's claw, "Pinchy" is controlling him.
- The events of The Missing Christmas Decorations and Day of the Diesels are mentioned.
- While the episode is called Diesel 10 is Back!, Splatter and Dodge also return.