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- “That's it! No more Mr. Nice Engine!”
At the Shunting Yards, Diesel is biffing Edward's trucks. Edward tells him not to, but Diesel insists it is the only way to get Troublesome Trucks to behave themselves.
Later, Diesel meets Hiro at Brendam Docks. Hiro is having trouble with his trucks so Diesel recommends biffing them to show them who's boss. Hiro tells Diesel that biffing trucks is never the right way and says it is always best to be kind and polite. Diesel is fed up with all the "Mr. Nice Engines" on the railway and couples up to the end of Hiro's train; he is going to show Hiro just how troublesome the trucks can be.
Going up a hill, Diesel - at the back of the train - applies his brakes. Hiro has to puff with all of his might to get his heavy train to the top. When they reach the top, Diesel pushes from the back and makes Hiro go very fast. Hiro and the trucks whoosh past Thomas who is very surprised to see Diesel at the back of the train and decides to follow Hiro.
Diesel biffs and bashes Hiro's train all the way to Knapford. Finally, Hiro loses patience and brakes sharply to give the trucks a bash. Milk churns are sent flying into the air and land near the Fat Controller, covering him and his assistants in milk. The milk also soaks Hiro and Edward.
Hiro feels terrible as the Fat Controller accuses him of causing confusion and delay. Diesel tries to sneak off before he is noticed, but Thomas arrives just as Diesel is about to do so and blocks him. Thomas reveals that Diesel had been pushing Hiro's train, much to Hiro's surprise. The Fat Controller reprimands Diesel and tells Hiro to show him how to look after trucks, to Hiro's pleasure.