Thomas and the Evil Diesel, retitled Thomas and the Naughty Diesel in American releases, is a book written by Christopher Awdry. It was later retitled Thomas and Diesel and included My First Thomas-style illustrations.
One morning, Percy is ill and has to go to the Works for repairs. The Fat Controller knew he had to borrow another engine to help out on Thomas' Branch Line, and unfortunately, Diesel is the only one available. He returns to Sodor to help out with the goods work on Thomas' Branch Line and, as expected, causes trouble for the engines by destroying the oldest and rudest truck in Ffarquhar Yards when the trucks were making fun of him for causing trouble back then. The Fat Controller is cross and immediately arranges for Diesel to go back home. But two days later, Thomas has an accident when Daisy drips her oil on the track he is taking and Clarabel's back wheels come off the rails at the special points at Dryaw. Diesel knew that the line Thomas is on is the only way he can get back home, so he comes to the rescue. Clarabel thanks him and asks the Fat Controller to forgive him, to which he rightfully does so, as the other engines do too. It seems that even Diesel has some good in him somewhere.
- Sir Topham Hatt
- Duck (absent in US release)
- Daisy (does not speak)
- Annie (does not speak)
- Bertie (does not speak, absent in US release)
- Gordon (cameo, absent in US release and My First Thomas release)
- The Random House version has less realistic illustrations and toned down dialogue.
- This marks Diesel's second appearance on Sodor.
- This book was written by request of the TV series producers, but was never adapted into an episode. However, Diesel being the only spare engine available was a plot device that Britt Allcroft would use in the TV series for the episode Diesel Does it Again. The World's Strongest Engine also uses this plot device.
- The Random House version, narrated by Robin Smith, was used as a bonus feature on the DVDs, Thomas Comes to Breakfast and Other Thomas Adventures and The Early Years (Disc 3).