The Lazy Diesel is a magazine story, illustrated using photographs from the television series.
One day, Dennis sees Thomas enjoying his day off. Lazy Dennis decides to pretend to have something wrong with him so that Thomas will do all of his work for him. Dennis starts puffing and huffing noisily, prompting Thomas to ask if he is alright. Dennis pretends he is overheating and Thomas says that it is his day off, but he will find another engine to help him.
Dennis is very cross; he had wanted Thomas to his work for him right then. So, Dennis decides to run away. He does not care about his trucks, only about getting as far away from his work as possible. Then, Dennis derails. He calls for help, but there is no-one there to hear him.
Meanwhile, Thomas meets Percy who informs him that Dennis is missing and his trucks are needed. Luckily, Thomas thinks he knows where Dennis is and he sets off. He is most surprised to find Dennis in a ditch. Dennis sadly admit that he had tricked Thomas and that there had been nothing wrong with him. Thomas helps Dennis back onto the track and to Bluff's Cove. Dennis thanks Thomas for helping him and showing him that being really useful is better than being really lazy.