Diesel Do Right is the ninth episode of the twenty-third series.
Diesel is cross about being in trouble with the Fat Controller after mistakenly taking some trucks to Whiff's Waste Dump instead of the docks like he was supposed to. Now having to, in Dart's words, fix his own problems, Diesel is upset over having to take trucks to Brendam the next day before starting his other jobs and over the fact that the other diesels do not seem to care about how it feels to be in trouble all the time. Sidney offers to help, but Den reminds him that he needs to collect parts to help repair Philip, who is waiting nearby.
While Diesel heads to the docks with his trucks the next day, he grumbles over the Fat Controller seemingly having it out for him in particular. He then overhears Rebecca tell Salty that she is always happy to help, which gives him an idea as to how to get the other diesels in trouble for a change. He pretends to desperately need help, which Rebecca is happy to give, and tells Rebecca to take the nearby engine parts mentioned before to McColl Farm. Since Paxton's load is there, Diesel then tells Rebecca to take the fruit and vegetables she will find there to the quarry. And since Norman's load is there, Diesel also tells Rebecca to take the stone she will find there to Vicarstown Yard. Ever eager to help, Rebecca does exactly what Diesel has told her to do.
Terence is staring at the flatbed of engine parts in bafflement when he hears Paxton ask where his fruit and vegetables bound for market are. As Terence tells him, Norman arrives at the quarry and asks where his load of stone headed for Ulfstead Castle is. Skarloey tells him that Rebecca collected it. Peter Sam adds that Rebecca left all the fruit and vegetables in front of them. At that moment, Sidney arrives at Vicarstown Yard, expecting to find steel to take to Brendam docks, but he does not see any steel there.
It is revealed that Rebecca took the steel to Ulfstead Castle, where Millie tells her that they need stone, not steel. Thanks to Millie, Rebecca realises that she should know better than to listen to Diesel and that she was not really helping. Diesel is chortling to himself while shunting, knowing that his plan worked. Paxton arrives at market and sees that the fruit and vegetables never arrived. Sidney tries to ask around the docks about his steel and flatbed of engine parts, but he cannot remember who the parts were for. They were for Philip, whom Den regrettably informs that they are unable to repair him. Dart clarifies that Sidney did not deliver the parts, which are still sitting abandoned at McColl Farm.
That night, Diesel is startled awake by the sound of the Fat Controller telling off Paxton and Sidney for not doing their jobs, as well as with the "usually so reliable" Norman. He declares that Philip has been hanging around all day and that Diesel is the only diesel who has done his job properly. Diesel says that it is just him trying to be useful as always, when Rebecca rushes in and bumps into Thomas. She tells Diesel about the confusion, which prompts the Fat Controller to ask her what else Diesel asked her to do in addition to taking the stone to Vicarstown. As Rebecca tells him, the other diesels realise what has happened and Diesel tries to slink back into the Dieselworks, away from the absolutely furious Fat Controller. His plan foiled, Diesel is upset that he is still the only one to be in trouble even when he is the only one who did not do anything wrong, or so he thinks.
- Peter Sam
- Sir Topham Hatt
- Farmer McColl (does not speak)
- Sir Handel (cameo)
- Duncan (cameo)
- Luke (cameo)
- Cranky (cameo)
- Big Mickey (cameo)
- Carly (cameo)
- Farmer Finney (cameo)
- Island of Sodor
- Vicarstown Dieselworks
- Vicarstown Diesel Sheds
- Diesel 10's Shed
- Brendam Docks
- Sodor Shipping Company
- McColl Farm
- Blue Mountain Quarry
- Vicarstown Yards
- Vicarstown Bridge
- Ulfstead Castle
- Knapford Yards
- Town Square
- The Cow Field (fantasy)
- Ffarquhar Quarry (fantasy)
- Wellsworth Scrap Yard (fantasy)
- Whiff's Waste Dump (mentioned)
- The Mainland (fantasy)
- The Experimental Engines Yard (fantasy)
- United States (fantasy)
- Joseph May as Thomas
- Kerry Shale as Diesel
- Keith Wickham as Salty, Den, Norman, Skarloey and Sir Topham Hatt
- Steven Kynman as Dart, Paxton and Peter Sam
- Bob Golding as Sidney
- Rachael Miller as Rebecca
- Tom Stourton as Terence
- Miranda Raison as Millie
- Rasmus Hardiker as Philip
- The title is likely a reference to the cartoon Dudley Do Right.
- Diesel's fantasy sequence is a parody of the current intro from Series 22 onwards.
- Apart from Thomas reading the title aloud, this episode does not include any narration.
- A callback from the twentieth series episode, Sidney Sings was made when Sidney sang the same song from the latter.
- This episode marks the first of a few things:
- Norman's first speaking role since the movie The Great Race, his first speaking role in an episode since the twentieth series episode, Sidney Sings and his first speaking role in an episode outside of stock footage since the seventeenth series episode, The Frozen Turntable.
- Peter Sam's first speaking role since the twentieth series episode, Saving Time.
- Tidmouth Town Square's first appearance since the twentieth series episode, Letters to Santa.
- This episode marks the only things for a few characters in the twenty-third series:
- Philip and Skarloey’s only speaking roles.
- Terence, Sir Handel, Peter Sam, and Farmer McColl’s only appearances.
- Throughout the fantasy sequence, the Dieselworks is miscoloured purple.