Thomas and the Naughty Diesel in the US known as Thomas and the Evil Diesel in the UK is an upcoming episode.
One morning, Percy is ill and has to go to the Works for repairs. Sir Topham Hatt knows he has 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 end up making fun of him for causing trouble back then. Sir Topham Hatt 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 knows 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 Sir Topham Hatt 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 and all the other engines are glad to see him again the next time he comes to Sodor.
- Annie and Clarabel
- Sir Topham Hatt
- Gordon (cameo)
- Nia (cameo)
- Rebecca (cameo)
- Stanley (stock footage)
- Slip Coaches (stock footage cameo)
- At the end of the episode, Thomas mentions the events from the twentieth season episode, Pouty James, stock footage from this episode is also used.