Air date: September 29, 1998 (UK)
Bill and Ben have been working hard in the clay mines and quarries near Brendam Docks. Their jobs are important and can make them naughty, especially when it is very hot and dirty for the twins.
One day, Bill and Ben indeed become very naughty and argue over who has rights to some trucks in front of them. When BoCo shows up he tells the twins to stop quarrelling and tries to warn the two of getting in trouble with the Fat Controller, but the two ignore him and collide into each other at the points when they both try to take the trucks. The Fat Controller eventually intervenes and warns Bill and Ben to behave better and threatens to send them to their sheds, should they persist. He then decides to send a diesel to help them, and hopes that he will make a good impression. BoCo also suggests that the twins just simply go back to work right away. Meanwhile, the Fat Controller has doubts about the idea; he is concerned that the new diesel may have teething troubles more than confusion.
The Fat Controller is right; the new diesel, Derek, is having issues while going up Gordon's Hill, and, while halfway up his engine coughs causing black smoke to billow out of his exhaust. BoCo is then prompted to rescue him, who apologises for the breakdown and explains he has teething troubles. The news soon spreads, and Thomas tells Percy about Derek's teething troubles. Percy misunderstands Thomas, and thinks this means the diesel has "toothache." Percy then tells Bill and Ben about Derek and wishes them good luck, as they know they need another to help out. The manager then arrives and sends the twins to take their loads from the quarry to the docks, where they will be resting as there is hard work to be done the next morning.
That evening, Bill and Ben take their loads to sidings by the quay and head off to the sheds where Duck is resting. Duck notices the twins' worried looks and tells the twins that "teething troubles" means that Derek is new but is having frequent breakdowns which (in his case) is his cooling system, making the twins even more nervous.
The next day, Bill and Ben prepare their load of trucks until Derek arrives at the Clay Pits and helps the twins with a long train of China Clay trucks by pushing from behind with Bill and Ben pulling at the front. However, during the journey, they come to a hill and another breakdown from Derek occurs from overheating. Bill and Ben pull him and the trucks and it works.
That night, the Fat Controller arrives at the sheds and congratulates Bill and Ben for their hard work and explains that Derek is sent to the works. The twins agree to manage their work alone and apologise to BoCo for being rude and explain that Derek was very friendly. Then Duck explains that friends always say goodnight to each other, and so they do, but all four engines still talk about Derek and his teething troubles all night long.
Tropes featured in the episode:
- All There in the Script: The new diesel's name is Derek, which is only revealed in merchandise.
- The Alleged Train: Derek is a Truth in Television example, as noted below.
- Argument of Contradictions: Bill and Ben argue about who gets the trucks.Bill: That's my line of trucks!
Ben: It's not! It's mine! Yours is over there!
Bill: It's mine!
Ben: It's not!
Bill: It's mine!
Ben: It's not! - Chuck Cunningham Syndrome: This episode marks BoCo's final appearance. For Derek, this was his only appearance.
- Lawyer-Friendly Cameo: This episode featured a BR "Clayton" diesel which, as in real life, suffered from having insufficient engines crammed into a compact space. While originally named "Paxman" after the contained engines, the producers decided the company might not take so kindly to the reference. He went unnamed in the episode, but the merchandise now calls him "Derek."
- Literal-Minded: Thomas mentions to Percy that Derek has teething troubles, but Percy believes he has a toothache.
- Random Events Plot: Derek has "teething troubles" due to his cooling system, the news spreads and Percy thinks that means the new diesel has a toothache, Derek breaks down while being the back engine for Bill and Ben's train so has to be pulled, and that night, Bill apologizes to BoCo for being rude, even though this was never shown to the audience.
