Donald and Douglas (now 9 and 10 respectively) realise that they only have numbers painted on their tenders, so no one would tell them apart otherwise. The inspector introduces them to Duck, who shows them around, and at night the twins put Gordon and Henry in their places when the two were teasing them about their whistles. One afternoon, Douglas is shunting in the yard and worries about being sent away, unfortunately causing him to forget to shunt Thomas' Special Coach. The twins decide to swap tenders so as to convince the Fat Controller that they have nothing to do with the coach going missing, but he is not fooled and severely reprimands Douglas.
- This episode was based on the story of the same name from The Railway Series book, The Twin Engines.
- In an interview with David Mitton released on SiF shortly before his death in 2008, he confirmed that the episode was in production and half way through filming when Britt Allcroft decided that it would be too confusing for children to understand. So as to prevent the season from being an episode short, the crew instead filmed Thomas, Percy and the Coal as a whole new episode. It is assumed that Donald and Douglas swapping tenders to attempt to fool the Fat Controller is what would have made the plot difficult to comprehend for children. Mitton also mentioned that he was in possession of all the original footage filmed for this episode.
- Six screenshots are all that is currently publicly visible of the filmed footage:
- A scene of Douglas shunting the coach can be seen in the 1989 annual.
- A close up of Douglas from the opening is seen in various books, posters, and on Douglas' Take-Along card (it is also seen on the cover to the New Zealand re-release of The Deputation and Other Stories on VHS).
- Various stills of the twins confronting Gordon and Henry at the sheds can be seen in a Japanese book and other merchandise.
- Another confirms Duck as a character, one shows an image of one of the Scottish twins beneath the coal hopper with Duck by his side, and the final shows a portion of the opening.
- Recently, the nephew of Britt Allcroft stated that she also had possession of the original footage.
- This is the first episode known to have been cancelled. However, the series pilot was never broadcast, but was re-shot as the twenty-fifth episode of the first season.
- Presumably, this episode was intended to air between Better Late Than Never and Break Van. Therefore, the episode Cows would have aired as the season's opener.
- The opening shot was used as stock footage in Break Van.
- Had this episode been filmed, it would have been the first and only appearance of Thomas' special coach in the television series. It would also have been the first episode to feature engines swapping tenders. However, in the tenth season episode It's Good to be Gordon, Gordon and Henry swap tenders, thus becoming the actual first episode with a tender swap instead.