- "Well, I'll eat my hat - if it isn't The Diesel!"
One day, the Fat Controller comes to see the engines with an announcement: a Railway Inspector is visiting that afternoon and another engine is coming to help them prepare for his arrival. The engines are excited, wondering who it could be.
Soon afterwards, a big green diesel arrives on Sodor, introducing himself as The Diesel. He is very rude to the steam engines, telling them they should be scrapped and replaced with diesels. The engines are very cross with him.
That afternoon, the Inspector arrives at the sheds when the Diesel races past. He is going so fast that the Inspector's hat is blown right off his head and into his air vents. The Diesel splutters to a stop and the Inspector scolds him for not being careful before sending him off to the repair yard. The Fat Controller orders Duck and Stepney to take his train instead.
The journey goes well for the two engines, and on their way back, they meet the Diesel again. The Diesel apologises for his behaviour, saying that he now thinks that steam engines are really useful too,
- Donald and Douglas
- The Diesel
- Sir Topham Hatt
- Thomas (cameo)
- Henry (cameo)
- Gordon (cameo)
- James (cameo)
- In the fourth illustration, Donald and Douglas are on different tracks to those in the third and fifth illustrations.