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 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 FfarquharYards when the trucks end up 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 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 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 and all the other engines are glad to see him again the next time he comes to Sodor.