Thomas and the Evil Diesel, retitled Thomas and the Naughty Diesel in American releases, is a tie-in book to The Railway Series written by Christopher Awdry and was published in 1987. It was later retitled Thomas and Diesel and included My First Thomas-style illustrations. The story focuses on Diesel who returns to Sodor to work at Thomas' Branch Line as Percy is sent to the works for repairs, but later on in the story had a change of heart after helping Thomas from an accident with the oily rails.
The book was primarily made as adaptation material for Thomas & Friends. Despite the novel being repackaged multiple times under the show's format however, it has never been made into an episode proper thus far.
This book contains examples of:
- Art Evolution: The original book was illustrated by Clive Spong in the same style he used for the main Railway Series books. It saw at least three redraws under the Thomas and Friends name, two with illustrations more in style with the original show, and a later one akin to the CGI episodes. A My First Thomas styled version was also released.
- Bittersweet Ending: Despite being sent back to the Other Railway for damaging the trucks, Diesel was sent away on a good note after helping Thomas, Annie, and Clarabel back on the rails. Now the other engines are glad to see him again the next time he comes to Sodor.
- Call-Back: Upon seeing Diesel, Duck is shocked and thought the Fat Controller had sent him away in disgrace.
- The Dog Bites Back : Diesel smashes the trucks through the buffers after they continuously and needlessly tease him for his past behavior.
- Help, I'm Stuck!: Thomas slips down into a siding, which led Clarabel get stuck in the mud off of the track.
- Jerkass: The Troublesome Trucks who mocked Diesel for his past actions until Diesel had enough of them.
- Jerk with a Heart of Gold: Diesel develops into one near the end of the book. He initially laughed upon hearing Thomas' predicament with Clarabel and only opted to rescue Thomas because the latter's train was blocking the line and preventing Diesel from going home, though he eventually realized that Good Feels Good.
- Never Trust a Title: Despite the title of the book, Diesel doesn't do anything particularly evil. The only "evil" thing he did was smash up some trucks for mocking him, and he redeemed himself in the end by helping out Thomas, Annie and Clarabel from an embankment.
- Reformed, but Rejected: Despite initially trying to behave and be polite (if in his usual oily way), Diesel wasn't received warmly by Thomas and Toby when he was brought back. It is only when Diesel does a legitimately good deed that he wins them over.
- Slippery Skid: 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.
- When He Smiles: Diesel in the book is painted with a sinister smile after returning, but after helping Thomas, Annie, and Clarabel, he shows a genuine smile.
