

Thomas was surprised at the train pushing him and Diesel was horrified, thinking Thomas was pulling the train, realising his chance would be ruined. When he whistled after a shunter coupled him up, the diesels mistook the tank engine's whistle as Diesel's horn and started pushing the train as they were instructed to. The day before the show, Diesel refused to move his train from blocking all ways in and out of the yard, leading Thomas - who was in a hurry to demonstrate his shunting skills to convince the Fat Controller to enter him in the shunting competition - to move Diesel's train himself. When the Fat Controller was in the final stages of choosing who would go to the show, Diesel would then honk his horn to signal the three to start pushing, making it look as if Diesel was moving the train by himself (whereas the other three diesels would actually be doing most of the work) which Diesel hoped would convince the Fat Controller to take him to the show. Diesel had the three put under crates in a large train, making them resemble vans.

In The Great Race, Den, Dart and Paxton were part of Diesel's plot to be taken to The Great Railway Show. When Mavis came back, Den went back to the Dieselworks. But after some encouragement from Toby and Henrietta, he toughened up and finished his job. Initially, Den struggled with the troublesome trucks. In the nineteenth series, he was sent to the quarry as a replacement for Mavis while she was at the Dieselworks. In the eighteenth series, Den, Dart, Sidney and Diesel hid from Paxton, causing Paxton to search for them. In the seventeenth series, Den (along with Dart) help fixed a sputter in Salty's engine. In the sixteenth series, he and Dart helped Thomas fix Ol' Wheezy and repaired Gordon's bufferbeam. Den later teased Flynn for spraying the Fat Controller and Gordon. In the fifteenth series, he, Dart and Diesel tried to find a Christmas tree for the Dieselworks whilst in competition with Thomas. In Day of the Diesels, Den and Dart took Thomas to the back shed of the Dieselworks while Percy, Diesel 10 and the other diesels took over the Steamworks.
